Semiconductor devices containing copper bonding pads with different conductive barrier layers and methods for forming the same

ABSTRACT

Bonding strength and yield can be enhanced by providing a mating pair of a convex bonding surface and a concave bonding surface. The convex bonding surface can be provided by employing a conductive barrier layer having a higher electrochemical potential than copper. The concave bonding surface can be provided by employing a conductive barrier layer having a lower electrochemical potential than copper. Alternatively additionally, a copper material portion in a bonding pad may include at least 10% volume fraction of (200) copper grains to provide high volume expansion toward a mating copper material portion. The mating copper material portion may be formed with at least 95% volume fraction of (111) copper grains to provide high surface diffusivity, or may be formed with at least 10% volume fraction of (200) copper grains to provide high volume expansion.

FIELD

The present disclosure relates generally to the field of semiconductordevices, and particularly to a semiconductor structure including abonded assembly of semiconductor dies that are bonded viacopper-to-copper bonding and methods for forming the same.

BACKGROUND

Process reliability and yield of copper-to-copper bonding between matingpairs of copper pads becomes more challenging as the dimensions of thecopper pads decrease in advanced semiconductor technology generations.Reducing volumes of cavities between mating pairs of copper pads isdesirable to improve copper-to-copper bonding during chip bonding.

SUMMARY

According to an aspect of the present disclosure, a bonded assemblycomprises a first semiconductor die comprising first semiconductordevices and a first bonding pad, wherein the first bonding pad comprisesa first copper material portion and a first conductive barrier layercomprising a first conductive barrier material having a higherelectrochemical potential than copper located between the firstsemiconductor devices and the first copper material portion, and asecond semiconductor die comprising second semiconductor devices and asecond bonding pad, wherein the second bonding pad comprises a secondcopper material portion and a second conductive barrier layer comprisinga second conductive barrier material having a lower electrochemicalpotential than copper located between the second semiconductor devicesand the second copper material portion. The second bonding pad is bondedto the first bonding pad.

According to another aspect of the present disclosure, a method offorming a bonded assembly is provided, which comprises: providing afirst semiconductor die comprising first semiconductor devices, firstmetal interconnect structures embedded in first dielectric materiallayers and electrically connected to the first semiconductor devices,and a first bonding pad embedded in a first bonding-level dielectriclayer and electrically connected to one of the first metal interconnectstructures, wherein the first bonding pad comprises a first conductivebarrier layer comprising a first conductive barrier material having ahigher electrochemical potential than copper and a first copper materialportion at least partially laterally surrounded by the first conductivebarrier layer; providing a second semiconductor die comprising secondsemiconductor devices, second metal interconnect structures embedded insecond dielectric material layers and electrically connected to thesecond semiconductor devices, and a second bonding pad embedded in asecond bonding-level dielectric layer and electrically connected to oneof the second metal interconnect structures, wherein the second bondingpad comprises a second conductive barrier layer comprising a secondconductive barrier material having a lower electrochemical potentialthan copper and a second copper material portion at least partiallylaterally surrounded by the second conductive barrier layer; and bondingthe second bonding pad to the first bonding pad by inducingcopper-to-copper bonding between the second copper material portion andthe first copper material portion.

According to an aspect of the present disclosure, a bonded assemblycomprises a first semiconductor die comprising first semiconductordevices and a first bonding pad, wherein the first bonding pad comprisesa first copper material portion containing (200) copper grains at avolume fraction of at least 10% and a first conductive barrier layerlocated between the first semiconductor devices and the first coppermaterial portion, and a second semiconductor die comprising secondsemiconductor devices and a second bonding pad, wherein the secondbonding pad comprises a second copper material portion and a secondconductive barrier layer located between the second semiconductordevices and the second copper material portion. The second bonding padis bonded to the first bonding pad.

According to another aspect of the present disclosure, a bonded assemblyis provided, which comprises: a first semiconductor die comprising firstsemiconductor devices, first metal interconnect structures embedded infirst dielectric material layers and electrically connected to the firstsemiconductor devices, and a first bonding pad embedded in a firstbonding-level dielectric layer and electrically connected to one of thefirst metal interconnect structures, wherein the first bonding padcomprises a first conductive barrier layer and a first copper materialportion at least partially laterally surrounded by the first conductivebarrier layer and including (200) copper grains at a volume fraction ofat least 10%; and a second semiconductor die comprising secondsemiconductor devices, second metal interconnect structures embedded insecond dielectric material layers and electrically connected to thesecond semiconductor devices, and a second bonding pad embedded in asecond bonding-level dielectric layer and electrically connected to oneof the second metal interconnect structures, wherein the second bondingpad comprises a second conductive barrier layer and a second coppermaterial portion at least partially laterally surrounded by the secondconductive barrier layer and including (200) copper grains at a volumefraction not less than 10%, wherein the second bonding pad is bonded tothe first bonding pad.

According to yet another aspect of the present disclosure, a method offorming a bonded assembly is provided, which comprises: providing afirst semiconductor die comprising first semiconductor devices, firstmetal interconnect structures embedded in first dielectric materiallayers and electrically connected to the first semiconductor devices,and a first bonding pad embedded in a first bonding-level dielectriclayer and electrically connected to one of the first metal interconnectstructures, wherein the first bonding pad comprises a first conductivebarrier layer and a first copper material portion laterally surroundedby the first conductive barrier layer and including (200) copper grainsat a volume fraction not less than 10%; providing a second semiconductordie comprising second semiconductor devices, second metal interconnectstructures embedded in second dielectric material layers andelectrically connected to the second semiconductor devices, and a secondbonding pad embedded in a second bonding-level dielectric layer andelectrically connected to one of the second metal interconnectstructures, wherein the second bonding pad comprises a second conductivebarrier layer and a second copper material portion laterally surroundedby the second conductive barrier layer; and bonding the second bondingpad is bonded to the first bonding pad by inducing copper-to-copperbonding between the second copper material portion and the first coppermaterial portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic vertical cross-sectional view of a firstconfiguration of a memory die after formation of memory-side padcavities according to a first embodiment of the present disclosure.

FIG. 1B is a schematic vertical cross-sectional view of the firstconfiguration of the memory die after formation of a memory-sideconductive barrier layer and a memory-side copper layer according to thefirst embodiment of the present disclosure.

FIG. 1C is a schematic vertical cross-sectional view of the firstconfiguration of the memory die along plane C-C′ in FIG. 1D afterformation of memory-side bonding pads according to the first embodimentof the present disclosure.

FIG. 1D is a schematic top-down view of the first configuration of thememory die after formation of the memory-side bonding pads according tothe first embodiment of the present disclosure.

FIG. 2A is a schematic vertical cross-sectional view of a secondconfiguration of a logic die after formation of logic-side pad cavitiesaccording to the first embodiment of the present disclosure.

FIG. 2B is a schematic vertical cross-sectional view of the secondconfiguration of the logic die after formation of a logic-sideconductive barrier layer and a logic-side copper layer according to thefirst embodiment of the present disclosure.

FIG. 2C is a schematic vertical cross-sectional view of the secondconfiguration of the logic die after formation of logic-side bondingpads according to the first embodiment of the present disclosure.

FIG. 2D is a schematic top-down view of the second configuration of thelogic die after formation of the logic-side bonding pads according tothe first embodiment of the present disclosure.

FIG. 3A is a schematic vertical cross-sectional view of a firstconfiguration of a first exemplary structure after the logic die isdisposed on the memory die for bonding according to the first embodimentof the present disclosure.

FIG. 3B is a schematic vertical cross-sectional view of the firstconfiguration of the first exemplary structure after bonding the logicdie to the memory die according to the first embodiment of the presentdisclosure.

FIGS. 3C and 3D are schematic vertical cross-sectional views ofalternative first configurations of the first exemplary structure afterthinning the memory die according to the first embodiment of the presentdisclosure.

FIG. 4A is a schematic vertical cross-sectional view of a secondconfiguration of the first exemplary structure after the logic die isdisposed on the memory die for bonding according to the first embodimentof the present disclosure.

FIG. 4B is a schematic vertical cross-sectional view of the secondconfiguration of the first exemplary structure after bonding the logicdie to the memory die according to the first embodiment of the presentdisclosure.

FIGS. 4C and 4D are schematic vertical cross-sectional views ofalternative second configurations of the first exemplary structure afterthinning the memory die according to the first embodiment of the presentdisclosure.

FIG. 5 is a schematic vertical cross-sectional view of a thirdconfiguration of a logic die after formation of logic-side bonding padsaccording to the first embodiment of the present disclosure.

FIG. 6A is a schematic vertical cross-sectional view of the thirdconfiguration of the first exemplary structure after bonding the logicdie to the memory die according to the first embodiment of the presentdisclosure.

FIG. 6B is a schematic vertical cross-sectional view of the thirdconfiguration of the first exemplary structure after thinning the memorydie and formation of external bonding structures according to the firstembodiment of the present disclosure.

FIG. 7A is a schematic vertical cross-sectional view of a fourthconfiguration of the first exemplary structure after bonding the logicdie to the memory die according to the first embodiment of the presentdisclosure.

FIG. 7B is a schematic vertical cross-sectional view of the fourthconfiguration of the first exemplary structure after thinning the memorydie and formation of external bonding structures according to the firstembodiment of the present disclosure.

FIG. 8A is a vertical cross-sectional view of a first configuration of amemory die after formation of a memory-side conductive barrier layer anda memory-side copper layer according to a second embodiment of thepresent disclosure.

FIG. 8B is a vertical cross-sectional view of the first configuration ofthe memory die after formation of a memory-side bonding pads accordingto a second embodiment of the present disclosure.

FIG. 9A is a vertical cross-sectional view of a first configuration of alogic die after formation of a logic-side conductive barrier layer and alogic-side copper layer according to a second embodiment of the presentdisclosure.

FIG. 9B is a vertical cross-sectional view of the first configuration ofthe logic die after formation of a logic-side bonding pads according toa second embodiment of the present disclosure.

FIG. 10A is a schematic vertical cross-sectional view of a firstconfiguration of a second exemplary structure after the logic die isdisposed on the memory die for bonding according to the secondembodiment of the present disclosure.

FIG. 10B is a schematic vertical cross-sectional view of the firstconfiguration of the second exemplary structure after bonding the logicdie to the memory die according to the second embodiment of the presentdisclosure.

FIGS. 10C and 10D are schematic vertical cross-sectional views ofalternative first configurations of the second exemplary structure afterthinning the memory die according to the second embodiment of thepresent disclosure.

FIG. 11A is a vertical cross-sectional view of a second configuration ofa logic die after formation of a logic-side conductive barrier layer anda logic-side copper layer according to a second embodiment of thepresent disclosure.

FIG. 11B is a vertical cross-sectional view of the second configurationof the logic die after formation of a logic-side bonding pads accordingto a second embodiment of the present disclosure.

FIG. 12A is a schematic vertical cross-sectional view of a secondconfiguration of a second exemplary structure after the logic die isdisposed on the memory die for bonding according to the secondembodiment of the present disclosure.

FIG. 12B is a schematic vertical cross-sectional view of the secondconfiguration of the second exemplary structure after bonding the logicdie to the memory die according to the second embodiment of the presentdisclosure.

FIG. 12C is a schematic vertical cross-sectional view of the secondconfiguration of the second exemplary structure after thinning thememory die and formation of external bonding structures according to thesecond embodiment of the present disclosure.

FIG. 13A is a vertical cross-sectional view of a third configuration ofa memory die after formation of a memory-side conductive barrier layerand a memory-side copper layer according to a second embodiment of thepresent disclosure.

FIG. 13B is a vertical cross-sectional view of the third configurationof the memory die after formation of a memory-side bonding padsaccording to a second embodiment of the present disclosure.

FIG. 14A is a schematic vertical cross-sectional view of a thirdconfiguration of a second exemplary structure after the logic die isdisposed on the memory die for bonding according to the secondembodiment of the present disclosure.

FIG. 14B is a schematic vertical cross-sectional view of the thirdconfiguration of the second exemplary structure after bonding the logicdie to the memory die according to the second embodiment of the presentdisclosure.

FIG. 14C is a schematic vertical cross-sectional view of the thirdconfiguration of the second exemplary structure after thinning thememory die and formation of external bonding structures according to thesecond embodiment of the present disclosure.

DETAILED DESCRIPTION

The embodiments of the present disclosure are directed to asemiconductor structure including a bonded assembly of semiconductordies that are bonded via copper-to-copper bonding and methods forforming the same. The different conductive barrier layers may be used invarious embodiments to increase copper bonding yield for the bonded. Thevarious aspects of embodiments of the present disclosure are describedin detail herebelow.

The drawings are not drawn to scale. Multiple instances of an elementmay be duplicated where a single instance of the element is illustrated,unless absence of duplication of elements is expressly described orclearly indicated otherwise. Ordinals such as “first,” “second,” and“third” are used merely to identify similar elements, and differentordinals may be used across the specification and the claims of theinstant disclosure. The term “at least one” element refers to allpossibilities including the possibility of a single element and thepossibility of multiple elements.

The same reference numerals refer to the same element or similarelement. Unless otherwise indicated, elements having the same referencenumerals are presumed to have the same composition and the samefunction. Unless otherwise indicated, a “contact” between elementsrefers to a direct contact between elements that provides an edge or asurface shared by the elements. If two or more elements are not indirect contact with each other or among one another, the two elementsare “disjoined from” each other or “disjoined among” one another. Asused herein, a first element located “on” a second element can belocated on the exterior side of a surface of the second element or onthe interior side of the second element. As used herein, a first elementis located “directly on” a second element if there exist a physicalcontact between a surface of the first element and a surface of thesecond element. As used herein, a first element is “electricallyconnected to” a second element if there exists a conductive pathconsisting of at least one conductive material between the first elementand the second element. As used herein, a “prototype” structure or an“in-process” structure refers to a transient structure that issubsequently modified in the shape or composition of at least onecomponent therein.

As used herein, a “layer” refers to a material portion including aregion having a thickness. A layer may extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer may bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer may be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer may extend horizontally, vertically, and/or along atapered surface. A substrate may be a layer, may include one or morelayers therein, or may have one or more layer thereupon, thereabove,and/or therebelow.

As used herein, a first surface and a second surface are “verticallycoincident” with each other if the second surface overlies or underliesthe first surface and there exists a vertical plane or a substantiallyvertical plane that includes the first surface and the second surface. Asubstantially vertical plane is a plane that extends straight along adirection that deviates from a vertical direction by an angle less than5 degrees. A vertical plane or a substantially vertical plane isstraight along a vertical direction or a substantially verticaldirection, and may, or may not, include a curvature along a directionthat is perpendicular to the vertical direction or the substantiallyvertical direction.

As used herein, a “memory level” or a “memory array level” refers to thelevel corresponding to a general region between a first horizontal plane(i.e., a plane parallel to the top surface of the substrate) includingtopmost surfaces of an array of memory elements and a second horizontalplane including bottommost surfaces of the array of memory elements. Asused herein, a “through-stack” element refers to an element thatvertically extends through a memory level.

As used herein, a “semiconducting material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0×10⁵ S/m.As used herein, a “semiconductor material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0 S/m in theabsence of electrical dopants therein, and is capable of producing adoped material having electrical conductivity in a range from 1.0 S/m to1.0×10⁵ S/m upon suitable doping with an electrical dopant. As usedherein, an “electrical dopant” refers to a p-type dopant that adds ahole to a valence band within a band structure, or an n-type dopant thatadds an electron to a conduction band within a band structure. As usedherein, a “conductive material” refers to a material having electricalconductivity greater than 1.0×10⁵ S/m. As used herein, an “insulatormaterial” or a “dielectric material” refers to a material havingelectrical conductivity less than 1.0×10⁻⁵ S/m. As used herein, a“heavily doped semiconductor material” refers to a semiconductormaterial that is doped with electrical dopant at a sufficiently highatomic concentration to become a conductive material either as formed asa crystalline material or if converted into a crystalline materialthrough an anneal process (for example, from an initial amorphousstate), i.e., to have electrical conductivity greater than 1.0×10⁵ S/m.A “doped semiconductor material” may be a heavily doped semiconductormaterial, or may be a semiconductor material that includes electricaldopants (i.e., p-type dopants and/or n-type dopants) at a concentrationthat provides electrical conductivity in the range from 1.0×10⁻⁵ S/m to1.0×10⁵ S/m. An “intrinsic semiconductor material” refers to asemiconductor material that is not doped with electrical dopants. Thus,a semiconductor material may be semiconducting or conductive, and may bean intrinsic semiconductor material or a doped semiconductor material. Adoped semiconductor material may be semiconducting or conductivedepending on the atomic concentration of electrical dopants therein. Asused herein, a “metallic material” refers to a conductive materialincluding at least one metallic element therein. All measurements forelectrical conductivities are made at the standard condition.

Generally, a semiconductor package (or a “package”) refers to a unitsemiconductor device that may be attached to a circuit board through aset of pins or solder balls. A semiconductor package may include asemiconductor chip (or a “chip”) or a plurality of semiconductor chipsthat are bonded throughout, for example, by flip-chip bonding or anotherchip-to-chip bonding. A package or a chip may include a singlesemiconductor die (or a “die”) or a plurality of semiconductor dies. Adie is the smallest unit that may independently execute externalcommands or report status. Typically, a package or a chip with multipledies is capable of simultaneously executing as many external commands asthe total number of planes therein. Each die includes one or moreplanes. Identical concurrent operations may be executed in each planewithin a same die, although there may be some restrictions. In case adie is a memory die, i.e., a die including memory elements, concurrentread operations, concurrent write operations, or concurrent eraseoperations may be performed in each plane within a same memory die. In amemory die, each plane contains a number of memory blocks (or “blocks”),which are the smallest unit that may be erased by in a single eraseoperation. Each memory block contains a number of pages, which are thesmallest units that may be selected for programming. A page is also thesmallest unit that may be selected to a read operation.

Referring to FIG. 1A, a memory die 900 is illustrated. First-typebonding pads, which are also referred to as first bonding pads, can besubsequently formed on the memory die 900. In this case, the memory die900 can be referred to as a first-type semiconductor die, or as a firstsemiconductor die 100. The memory die 900 includes a memory-sidesubstrate 908, memory-side semiconductor devices 920 overlying thememory-side substrate 908, memory-side dielectric material layers (290,950) located on the memory-side semiconductor devices, and memory-sidemetal interconnect structures 960 embedded in the memory-side dielectricmaterial layers (290, 950). In one embodiment, the memory-side substrate908 may be a portion of a commercially available silicon wafer having athickness in a range from 500 microns to 1 mm. In one embodiment, aplurality of first semiconductor dies 100 can be provided on thememory-side substrate 908, which may be a single crystal silicon wafer,or another suitable substrate.

Optional discrete substrate recess cavities can be formed in an upperportion of the memory-side substrate 908 by applying a photoresist layerover the top surface of the memory-side substrate 908, lithographicallypatterning the photoresist layer to form an array of discrete openings,and transferring the pattern of the array of discrete openings into theupper portion of the memory-side substrate by performing an anisotropicetch process. The photoresist layer can be subsequently removed, forexample, by ashing. The depth of each discrete substrate recess cavitycan be in a range from 500 nm to 10,000, although lesser and greaterdepths can also be employed. Optional through-substrate liner 386 andoptional through-substrate via structure 388 can be formed within eachdiscrete substrate recess cavity.

Generally, the memory-side semiconductor devices 920 may comprise anysemiconductor device known in the art. In one embodiment, the memory die900 comprises a memory die, and may include memory devices, such as athree-dimensional NAND memory device. In an illustrative example, thememory-side semiconductor devices 920 may include a verticallyalternating stack of insulating layers 32 and electrically conductivelayers 46, and a two-dimensional array of memory openings verticallyextending through the vertically alternating stack (32, 46). Theelectrically conductive layers 46 may comprise word lines of thethree-dimensional NAND memory device.

A memory opening fill structure 58 may be formed within each memoryopening. A memory opening fill structure 58 may include a memory filmand a vertical semiconductor channel contacting the memory film. Thememory film may include a blocking dielectric, a tunneling dielectricand a charge storage material located between the blocking and tunnelingdielectric. The charge storage material may comprise charge trappinglayer, such as a silicon nitride layer, or a plurality of discretecharge trapping regions, such as floating gates or discrete portions ofa charge trapping layer. In this case, each memory opening fillstructure 58 and adjacent portions of the electrically conductive layers46 constitute a vertical NAND string. Alternatively, the memory openingfill structures 58 may include any type of non-volatile memory elementssuch as resistive memory elements, ferroelectric memory elements, phasechange memory elements, etc. The memory device may include an optionalhorizontal semiconductor channel layer 10 connected to the bottom end ofeach vertical semiconductor channel, and an optional dielectric spacerlayer 910 that provides electrical isolation between the memory-sidesubstrate 908 and the horizontal semiconductor channel layer 10.

The electrically conductive layers 46 may be patterned to provide aterrace region in which each overlying electrically conductive layer 46has a lesser lateral extent than any underlying electrically conductivelayer 46. Contact via structures (not shown) may be formed on theelectrically conductive layers 46 in the terrace region to provideelectrical connection to the electrically conductive layers 46.Dielectric material portions 65 may be formed around each verticallyalternating stack (32, 46) to provide electrical isolation betweenneighboring vertically alternating stacks (32, 46).

Through-memory-level via cavities can be formed through the dielectricmaterial portions 65, the optional dielectric spacer layer 910, and thehorizontal semiconductor channel layer 10. An optionalthrough-memory-level dielectric liner 486 and a through-memory-level viastructure 488 can be formed within each through-memory-level via cavity.Each through-memory-level dielectric liner 486 includes a dielectricmaterial such as silicon oxide. Each through-memory-level via structure488 can be formed directly on a respective one of the through-substratevia structure 388.

The memory-side dielectric material layers (290, 950) may includememory-side proximal dielectric material layers 290 embedding contactvia structures and bit lines 962 and memory-side distal dielectricmaterial layers 950 that embed a subset of the memory-side metalinterconnect structures 960 located above the memory-side proximaldielectric material layers 290. As used herein, a “proximal” surfacerefers to a surface that is close to a substrate, and a “distal” surfacerefers to a surface that is distal from the substrate. In the memory die900, a proximal surface refers to a surface that is close to thememory-side substrate 908, and a distal surface refers to a surface thatis distal from the memory-side substrate 908.

The bit lines 962 may electrically contact drain regions located abovethe semiconductor channel at the top of the memory opening fillstructures 58. The contact via structures contact various nodes of thememory-side semiconductor devices, such as the electrically conductivelayers 46 (e.g., word lines and select gate electrodes). Generally, thememory-side metal interconnect structures 960 can be electricallyconnected to the memory-side semiconductor devices 920.

Each of the memory-side proximal dielectric material layers 290 and thememory-side distal dielectric material layers 950 may include adielectric material such as undoped silicate glass, a doped silicateglass, organosilicate glass, silicon nitride, a dielectric metal oxide,or a combination thereof. The memory-side distal dielectric materiallayers 950 may include one or more dielectric diffusion barrier layers(not expressly shown). In this case, each dielectric diffusion barrierlayer embedded in the memory-side distal dielectric material layers 950may include silicon carbon nitride (i.e., silicon carbonitride “SiCN”,which is also referred to silicon carbide nitride), silicon nitride(Si₃N₄), silicon oxynitride, or any other dielectric material that iseffective in blocking diffusion of copper. In one embodiment, eachdielectric diffusion barrier layer embedded in the memory-side distaldielectric material layers 950 may include a dielectric material havinga dielectric constant less than 5, such as SiCN having a dielectricconstant of about 3.8, to reduce RC delay of the memory-side metalinterconnect structures 960. Each dielectric diffusion barrier layer mayhave a thickness in a range from 10 nm to 30 nm.

An optional memory-side dielectric diffusion barrier layer 952 can beformed over the memory-side dielectric material layers (290, 950). Thememory-side dielectric diffusion barrier layer 952 can include adielectric material that blocks copper diffusion. In one embodiment, thememory-side dielectric diffusion barrier layer 952 can include siliconnitride, silicon carbon nitride, silicon oxynitride, or a stack thereof.The thickness of the memory-side dielectric diffusion barrier layer 952can be in a range from 5 nm to 50 nm, although lesser and greaterthicknesses can also be employed.

A memory-side bonding-level dielectric layer 970 can be formed over thememory-side dielectric diffusion barrier layer 952. In case firstbonding pads are subsequently formed in the memory-side bonding-leveldielectric layer 970, the memory-side bonding-level dielectric layer 970is herein referred to as a first bonding-level dielectric layer.Optionally, the memory-side bonding-level dielectric layer 970 mayinclude a dielectric material that permits dielectric-to-dielectricbonding. The memory-side bonding-level dielectric layer 970 may include,and/or consist essentially of, undoped silicate glass (i.e., siliconoxide), a doped silicate glass, organosilicate glass, silicon nitride,or a dielectric metal oxide. The thickness of the memory-sidebonding-level dielectric layer 970 may be in a range from 300 nm to3,000 nm, although lesser and greater thicknesses may also be employed.The memory-side bonding-level dielectric layer 970 may have a planar topsurface.

A photoresist layer (not shown) can be applied over the memory-sidebonding-level dielectric layer 970, and can be lithographicallypatterned to form discrete openings in each area in which first bondingpads are to be subsequently formed. In one embodiment, the first bondingpads may have shape similar to a mushroom including a lower via (e.g.,stem) portion and an upper plate (e.g., cap) portion having a greaterlateral dimension than the lower via portion. In this case, discreteopening in the photoresist layer can have shapes of the lower viaportions of the first bonding pads. A first anisotropic etch process canbe performed to transfer the pattern of the openings in the photoresistlayer into an upper portion of the memory-side bonding-level dielectriclayer 970. Recess cavities can be formed within unmasked areas in theupper portion of the memory-side bonding-level dielectric layer 970. Thephotoresist layer may be subsequently isotropically trimmed to increasethe size of each opening in the photoresist layer. Alternatively, thephotoresist layer may be removed and a new photoresist layer may beapplied and patterned over the memory-side bonding-level dielectriclayer 970 to form larger openings having peripheries that are laterallyoffset outward from a periphery of a respective recess cavity in theupper portion of the memory-side bonding-level dielectric layer 970. Asecond anisotropic etch process can be performed to etch portions of thememory-side bonding-level dielectric layer 970 that are not covered bythe photoresist layer. Memory-side pad cavities 979 are formed throughthe memory-side bonding-level dielectric layer 970 underneath discreteopenings in the photoresist layer. The photoresist layer may besubsequently removed, for example, by ashing.

Yet alternatively, the first bonding pads may be formed with arespective straight sidewall that vertically extends from a top surfaceof the memory-side bonding-level dielectric layer 970 to a bottomsurface of the memory-side bonding-level dielectric layer 970. In thiscase, the memory-side pad cavities 979 may be formed by applying andpatterning a photoresist layer, and by removing portions of thememory-side bonding-level dielectric layer 970 by performing ananisotropic etch process. In other words, a combination of a singlelithographic patterning process and a single anisotropic etch processmay be employed to form the memory-side pad cavities 979 with straightsidewall(s). In one embodiment, a lateral dimension (such as a diameteror a lateral distance between facing sides of a periphery) of eachopening in the photoresist layer may be in a range from 200 nm to 30microns, such as from 400 nm to 20 microns, although lesser and greaterdimensions may also be employed.

A top surface of a respective memory-side metal interconnect structure960 can be physically exposed at the bottom of each memory-side padcavity 979. In one embodiment, each memory-side pad cavity 979 can havea top periphery having a horizontal cross-sectional shape of a rectangleor a rounded rectangle. A maximum lateral dimension of each memory-sidepad cavity 979 may be in a range from 200 nm to 30 microns, such as from400 nm to 10 microns, although lesser and greater dimensions may also beemployed. Sidewalls of the memory-side pad cavities 979 may be vertical,or may have a taper angle greater than 0 degree and less than 30 degrees(such as a taper angle in a range from 3 degrees to 10 degrees) withrespect to the vertical direction. In case first bonding pads (e.g.,first-type bonding pads) are subsequently formed in the memory-side padcavities 979, the memory-side pad cavities 979 are herein referred to asfirst pad cavities.

Referring to FIG. 1B, a memory-side conductive (i.e., electricallyconductive) barrier layer 984L and a memory-side copper layer 986L canbe sequentially deposited in the memory-side pad cavities 979. In oneembodiment, the memory-side conductive barrier layer 984L may be formedas a first-type conductive barrier layer, which is herein referred to asa first conductive barrier layer 14L. In this case, the memory-sidecopper layer 986L is formed on the first conductive barrier layer 14L,and is herein referred to as a first copper layer 16L.

According to an aspect of the present disclosure, the first conductivebarrier layer 14L comprises, and/or consists essentially of, a firstconductive barrier material having a higher electrochemical potentialthan copper. Electrochemical potential is the mechanical work done inbringing 1 mole of an ion from a standard state to a specifiedconcentration and electrical potential. International Union of Pure andApplied Chemistry defines the electrochemical potential as the partialmolar Gibbs energy of a substance at the specified electric potential,where the substance is in a specified phase. In the present disclosure,all electric potentials are zero, and all materials are in a solid phasefor the purpose of calculation of electrochemical potential. Generally,electrochemical potential can be expressed as:

μ _(i)=μ_(i) +z _(i) FΦ,

in which μ _(i) is the electrochemical potential of species i, in J/mol,μ_(i) is the chemical potential of the species i, in J/mol, z_(i) is thevalency (charge) of the ion i, a dimensionless integer, F is the Faradayconstant, in C/mol, Φ is the local electrostatic potential, in V. In thespecial case of an uncharged atom, z_(i)=0, and so μ _(i)=μ_(i), whichis the case for all materials under discussion in the presentdisclosure. In other words, the electrochemical potential for allmaterial portions of the present disclosure is the chemical potential ofa respective material portion for the purpose of the present disclosurebecause all material portions are at an equipotential state.

Non-limiting examples of electrically conductive materials that providehigher electrochemical potential than copper and provide suitableadhesion strength to a dielectric material (such as silicon oxide) ofthe first bonding-level dielectric layer (such as the memory-sidebonding-level dielectric layer 970) comprise cobalt, tantalum, ortantalum nitride. In one embodiment, the first conductive barrier layer14 consists essentially of a material selected from cobalt, tantalum, ortantalum nitride. The thickness of the first conductive barrier layer14L (e.g., the memory-side conductive barrier layer 984L) may be in arange from 3 nm to 30 nm, such as from 6 nm to 20 nm, although lesserand greater thicknesses can also be employed.

The first copper layer 16L (e.g., memory-side copper layer 986L) mayconsist essentially of copper. The first copper layer 16L may be formedby depositing a copper seed layer (which is a lower surface portion ofthe first copper layer 16L) employing a physical vapor depositionprocess, and by depositing a copper fill material layer employingelectroplating. The thickness of the copper seed layer may be in a rangefrom 10 nm to 100 nm, and the thickness of the copper fill materiallayer, and measured over the top surface of the first bonding-leveldielectric layer, may be in a range from 300 nm to 6,000 nm, althoughlesser and greater thicknesses may also be employed.

Referring to FIGS. 1C and 1D, a first chemical mechanical polishing(CMP) process can be performed to remove portions of the first copperlayer 16L (e.g., the memory-side copper layer 986L) and the firstconductive barrier layer 14L (e.g., the memory-side conductive barrierlayer 984L) from above the top surface of the first bonding-leveldielectric layer (e.g., the memory-side bonding-level dielectric layer970). Each remaining portion of the first copper layer 16L comprises thefirst copper material portion 16. Each remaining portion of the firstconductive barrier layer 14L comprises a first conductive barrier layer14. Each first copper material portion 16 in this embodiment is amemory-side copper material portion 986. Each first conductive barrierlayer 14L in this embodiment is a memory-side conductive barrier layer984 embedded within the memory-side bonding dielectric layer 970. Eachcontiguous combination of a first conductive barrier layer 14 and afirst copper material portion 16 constitutes a first bonding pad 18,which in this embodiment is a memory-side bonding pad 988.

Generally, first bonding pads 18 embedded in a first bonding-leveldielectric layer (such as the memory-side bonding-level dielectric layer970) and electrically connected to a respective one of the first metalinterconnect structures (such as the memory-side metal interconnectstructures 960) are formed. Each of the first bonding pads 18 comprisesa first conductive barrier layer 14 including, and/or consistingessentially of, a first conductive barrier material having a higherelectrochemical potential than copper. Each of the first bonding pads 18comprises a first copper material portion 16 laterally surrounded by thefirst conductive barrier layer 14.

The first chemical mechanical polishing process proceeds under acondition in which the first conductive barrier material of the firstconductive barrier layer 14 has a higher electrochemical potential thancopper of the first copper material portion 16 within each first bondingpad 18. Generally, dissimilar metals and alloys have different electrodepotentials due to the differences in electrochemical potentials. Whentwo or more conductors having different electrochemical potentials comeinto contact in an electrolyte, such as a slurry in a chemicalmechanical polishing process, the more reactive conductor acts as anodeand the less reactive conductor acts as cathode for a galvanic reaction.During the first chemical mechanical polishing process, the firstconductive barrier layer 14 functions as an anode, and the first coppermaterial portion 16 functions as a cathode. Electrons flow (i.e.,current flows) from the first conductive barrier layer 14 to the firstcopper material portion 16 within each first bonding pad 18. The firstconductive barrier layer 14 is positively charged, and surface portionsof the first conductive barrier layer 14 in contact with the slurrygenerate positive ions of the metal within the first conductive barrierlayer 14. As a consequence, metal ions at the surface of the firstconductive barrier layer 14 that contact the slurry dissociate from thefirst conductive barrier layer 14, and diffuse into the slurry duringthe first chemical mechanical polishing process. A moat-shaped grooveregion 14G, which is also referred to as a “fang region,” can be formedin an upper portion of each first conductive barrier layer 14 that isphysically exposed to the slurry during the first chemical mechanicalpolishing process.

A concave top surface of the first conductive barrier layer 14 isvertically recessed relative to a periphery of a top surface of andadjoining portion of the first copper material portion 16 within eachmoat-shaped groove 14G. The moat-shaped groove 14G is formed around thefirst copper material portion 16 such that the moat-shaped groove 14Gencircles the periphery of an upper region of the first copper materialportion 16. The depth of each moat-shaped groove 14G, as measured alongthe vertical direction from the horizontal plane including the topsurface of the first bonding-level dielectric layer to the deepest pointin the moat-shaped groove 14G, may be in a range from 1 nm to 20 nm,such as from 2 nm to 10 nm, although lesser and greater depths may alsobe employed.

In one embodiment, a top surface of each first copper material portion16 may be formed with a convex vertical cross-sectional profile suchthat a center region of the top surface protrudes farther outward fromthe horizontal plane including the bottom surface of the firstbonding-level dielectric layer than a peripheral region of the topsurface of first copper material portion 16. The loss of material fromthe first conductive barrier layer 14 within each first bonding pad 18causes the generally convex profile of the top surface of the firstcopper material portion 16. In one embodiment, at least 50% of the areaof the top surface of each first copper material portion 16 may protrudeoutward from the horizontal plane including the top surface of the firstbonding-level dielectric layer (such as the memory-level dielectricmaterial layer 970).

Generally, a first semiconductor die 100 comprises first semiconductordevices, first metal interconnect structures embedded in firstdielectric material layers and electrically connected to the firstsemiconductor devices, and at least one first bonding pad 18 embedded ina first bonding-level dielectric layer and electrically connected to oneof the first metal interconnect structures. Each of the at least onefirst bonding pad 18 comprises a first conductive barrier layer 14comprising a first conductive barrier material having a higherelectrochemical potential than copper and a first copper materialportion 16 laterally surrounded by the first conductive barrier layer14. Optionally, a suitable pre-anneal bonding process may be performed,for example, at a temperature of about 150 degrees Celsius.

Referring to FIG. 2A, a first configuration of a logic die 700 accordingto the first embodiment of the present disclosure is illustrated.Second-type bonding pads, which are also referred to as second bondingpads, can be subsequently formed on the logic die 700. In this case, thelogic die 700 can be referred to as a second-type semiconductor die, oras a second semiconductor die 200. The logic die 700 includes alogic-side substrate 708, logic-side semiconductor devices 720 overlyingthe logic-side substrate 708, logic-side dielectric material layers 750located on the logic-side semiconductor devices, and logic-side metalinterconnect structures 760 embedded in the logic-side dielectricmaterial layers 750. In one embodiment, the logic-side substrate 708 maybe a commercially available single crystal silicon wafer. In oneembodiment, a plurality of second semiconductor dies 200 may be providedon the logic-side substrate 708.

Generally, the logic-side semiconductor devices may comprise anysemiconductor devices, such as field effect transistors in a CMOSconfiguration, that may be operated in conjunction with the memory-sidesemiconductor devices in the memory die 900 to provide enhancedfunctionality. In one embodiment, the logic die 700 comprises a supportcircuitry (i.e., a driver/peripheral circuitry) for operation of memorydevices (such as a three-dimensional array of memory elements) 920within the memory die 900. In one embodiment, the memory die 900 mayinclude a three-dimensional memory device 920 including athree-dimensional array of memory elements, word lines (that maycomprise a subset of the electrically conductive layers 46), and bitlines 962, and the logic-side semiconductor devices 720 of the logic die700 may include a peripheral circuitry for operation of thethree-dimensional array of memory elements. The peripheral circuitry mayinclude one or more word line driver circuits that drive the word linesof the three-dimensional array of memory elements of the memory die 900,one or more bit line driver circuits that drive the bit lines 962 of thememory die 900, one or more word line decoder circuits that decode theaddresses for the word lines, one or more bit line decoder circuits thatdecode the addresses for the bit lines 962, one or more sense amplifiercircuits that sense the states of memory elements within the memoryopening fill structures 58 of the memory die 900, a source power supplycircuit that provides power to the horizontal semiconductor channellayer 10 in the memory die 900, a data buffer and/or latch, and/or anyother semiconductor circuit that may be used to operatethree-dimensional memory device of the memory die 900.

The logic-side dielectric material layers 750 may include a dielectricmaterial such as undoped silicate glass, a doped silicate glass,organosilicate glass, silicon nitride, a dielectric metal oxide, or acombination thereof. The logic-side dielectric material layers 750 mayinclude one or more dielectric diffusion barrier layers (not expresslyshown). In this case, each dielectric diffusion barrier layer embeddedin the logic-side distal dielectric material layers 750 may includesilicon carbon nitride (i.e., silicon carbonitride “SiCN”, which is alsoreferred to silicon carbide nitride), silicon nitride (Si₃N₄), siliconoxynitride, or any other dielectric material that is effective inblocking diffusion of copper. In one embodiment, each dielectricdiffusion barrier layer embedded in the logic-side distal dielectricmaterial layers 750 may include a dielectric material having adielectric constant less than 5, such as SiCN having a dielectricconstant of about 3.8, to reduce RC delay of the logic-side metalinterconnect structures 760. Each dielectric diffusion barrier layer mayhave a thickness in a range from 20 nm to 30 nm.

An optional logic-side dielectric diffusion barrier layer 752 can beformed over the logic-side dielectric material layers 750. Thelogic-side dielectric diffusion barrier layer 752 can include adielectric material that blocks copper diffusion. In one embodiment, thelogic-side dielectric diffusion barrier layer 752 can include siliconnitride, silicon carbon nitride, silicon oxynitride, or a stack thereof.The thickness of the logic-side dielectric diffusion barrier layer 752can be in a range from 5 nm to 50 nm, although lesser and greaterthicknesses can also be employed.

A logic-side bonding-level dielectric layer 770 can be formed over thelogic-side dielectric diffusion barrier layer 752. In case secondbonding pads are subsequently formed in the logic-side bonding-leveldielectric layer 770, the logic-side bonding-level dielectric layer 770is herein referred to as a second bonding-level dielectric layer. In oneembodiment, the logic-side bonding-level dielectric layer 770 mayinclude a dielectric material that permits dielectric-to-dielectricbonding. The logic-side bonding-level dielectric layer 770 may include,and/or consist essentially of, undoped silicate glass (i.e., siliconoxide), a doped silicate glass, organosilicate glass, silicon nitride,or a dielectric metal oxide. The thickness of the logic-sidebonding-level dielectric layer 770 may be in a range from 300 nm to3,000 nm, although lesser and greater thicknesses may also be employed.The logic-side bonding-level dielectric layer 770 may have a planar topsurface.

A photoresist layer (not shown) can be applied over the logic-sidebonding-level dielectric layer 770, and can be lithographicallypatterned to form discrete openings in each area in which second bondingpads are to be subsequently formed. In one embodiment, the secondbonding pads may have shape similar to a mushroom including a lower via(e.g., stem) portion and an upper plate (e.g., cap) portion having agreater lateral dimension than the lower via portion. In this case,discrete opening in the photoresist layer can have shapes of the lowervia portions of the second bonding pads. A first anisotropic etchprocess can be performed to transfer the pattern of the openings in thephotoresist layer into an upper portion of the logic-side bonding-leveldielectric layer 770. Recess cavities can be formed within unmaskedareas in the upper portion of the logic-side bonding-level dielectriclayer 770. The photoresist layer may be subsequently isotropicallytrimmed to increase the size of each opening in the photoresist layer.Alternatively, the photoresist layer may be removed and a newphotoresist layer may be applied and patterned over the logic-sidebonding-level dielectric layer 770 to form larger openings havingperipheries that are laterally offset outward from a periphery of arespective recess cavity in the upper portion of the logic-sidebonding-level dielectric layer 770. A second anisotropic etch processcan be performed to etch portions of the logic-side bonding-leveldielectric layer 770 that are not covered by the photoresist layer.Logic-side pad cavities 779 are formed through the logic-sidebonding-level dielectric layer 770 underneath discrete openings in thephotoresist layer. The photoresist layer may be subsequently removed,for example, by ashing.

Yet alternatively, the second bonding pads may be formed with arespective straight sidewall that vertically extend from a top surfaceof the logic-side bonding-level dielectric layer 770 to a bottom surfaceof the logic-side bonding-level dielectric layer 770. In this case, thelogic-side pad cavities 779 may be formed by applying and patterning aphotoresist layer, and by removing portions of the logic-sidebonding-level dielectric layer 770 by performing an anisotropic etchprocess. In other words, a combination of a single lithographicpatterning process and a single anisotropic etch process may be employedto form the logic-side pad cavities 779 with straight sidewall(s). Inone embodiment, a lateral dimension (such as a diameter or a lateraldistance between facing sides of a periphery) of each opening in thephotoresist layer may be in a range from 200 nm to 30 microns, such asfrom 400 nm to 20 microns, although lesser and greater dimensions mayalso be employed.

A top surface of a respective logic-side metal interconnect structure760 can be physically exposed at the bottom of each logic-side padcavity 779. In one embodiment, each logic-side pad cavity 779 can have atop periphery having a horizontal cross-sectional shape of a rectangleor a rounded rectangle. A maximum lateral dimension of each logic-sidepad cavity 779 may be in a range from 200 nm to 30 microns, such as from400 nm to 20 microns, although lesser and greater dimensions may also beemployed. Sidewalls of the logic-side pad cavities 779 may be vertical,or may have a taper angle greater than 0 degree and less than 30 degrees(such as a taper angle in a range from 3 degrees to 20 degrees) withrespect to the vertical direction. In case second bonding pads (i.e.,second-type bonding pads) are subsequently formed in the logic-side padcavities 779, the logic-side pad cavities 779 are herein referred to assecond pad cavities.

Referring to FIG. 2B, a logic-side conductive barrier layer 784L and alogic-side copper layer 786L can be sequentially deposited in thelogic-side pad cavities 779. In one embodiment, the logic-sideconductive barrier layer 784L may be formed as a second-type conductivebarrier layer, which is herein referred to as a second conductivebarrier layer 24L. In this case, the logic-side copper layer 786L isformed on the second conductive barrier layer 24L, and is hereinreferred to as a second copper layer 26L.

According to an aspect of the present disclosure, the second conductivebarrier layer 24L comprises, and/or consists essentially of, a secondconductive barrier material having a lower electrochemical potentialthan copper. Non-limiting examples of metallic materials that provide alower electrochemical potential than copper and provide suitableadhesion strength to a dielectric material (such as silicon oxide) ofthe second bonding-level dielectric layer (such as the logic-sidebonding-level dielectric layer 770) comprise ruthenium, titanium, ortitanium nitride. In one embodiment, the second conductive barrier layer24 consists essentially of a material selected from ruthenium, titanium,or titanium nitride. The thickness of the second conductive barrierlayer 24L (which comprises the logic-side conductive barrier layer 784L)may be in a range from 3 nm to 30 nm, such as from 6 nm to 20 nm,although lesser and greater thicknesses can also be employed.

The second copper layer 26L (which comprises the logic-side copper layer786L) may consist essentially of copper. The second copper layer 26L maybe formed by depositing a copper seed layer (which is a lower surfaceportion of the second copper layer 26L) employing a physical vapordeposition process, and by depositing a copper fill material layeremploying electroplating. The thickness of the copper seed layer may bein a range from 20 nm to 200 nm, and the thickness of the copper fillmaterial layer, and measured over the top surface of the secondbonding-level dielectric layer, may be in a range from 300 nm to 6,000nm, although lesser and greater thicknesses may also be employed.

Referring to FIGS. 2C and 2D, a second chemical mechanical polishing(CMP) process can be performed to remove portions of the second copperlayer 26L (comprising the logic-side copper layer 786L) and the secondconductive barrier layer 24L (comprising the logic-side conductivebarrier layer 784L) from above the top surface of the secondbonding-level dielectric layer (comprising the logic-side bonding-leveldielectric layer 770). Each remaining portion of the second copper layer26L comprises the second copper material portion 26. Each remainingportion of the second conductive barrier layer 24L comprises a secondconductive barrier layer 24. Each second copper material portion 26 is alogic-side copper material portion 786. Each second conductive barrierlayer 24 is a logic-side conductive barrier layer 784 embedded withinthe logic-side bonding dielectric layer 770. Each contiguous combinationof a second conductive barrier layer 24 and a second copper materialportion 26 constitutes a second bonding pad 28, which in this embodimentis a logic-side bonding pad 788.

Generally, second bonding pads 28 embedded in a second bonding-leveldielectric layer (such as the logic-side bonding-level dielectric layer770) and electrically connected to a respective one of the second metalinterconnect structures (such as the logic-side metal interconnectstructures 760) are formed. Each of the second bonding pads 28 comprisesa second conductive barrier layer 24 including and/or consistingessentially of a second conductive barrier material having a lowerelectrochemical potential than copper. Each of the second bonding pads28 comprises a second copper material portion 26 laterally surrounded bythe second conductive barrier layer 24.

The second chemical mechanical polishing process proceeds under acondition in which the second conductive barrier material of the secondconductive barrier layer 24 has a lower electrochemical potential thancopper of the second copper material portion 26 within each secondbonding pad 28. During the second chemical mechanical polishing processof the present disclosure, the second conductive barrier layer 26functions as a cathode, and the second copper material portion 26functions as an anode. Electrons flow (i.e., current flows) from thesecond copper material portion 26 to the second conductive barrier layer24 within each first bonding pad 18. The second copper material portion26 is positively charged, and surface portions of the second copperportion 26 in contact with the slurry generate positive copper ions. Asa consequence, the copper ions at the surface of the second coppermaterial portion 26 that contact the slurry dissociate from the secondcopper portion 26, and diffuse into the slurry during the secondchemical mechanical polishing process, which results in dishing. Dishingleads to a concave upper surface in the second copper portion 26.

In one embodiment, the top surface of each second conductive barrierlayer 24 may be formed within a horizontal plane including the topsurface of the second bonding-level dielectric layer (which comprisesthe logic-side bonding-level dielectric layer 770). In one embodiment,each second conductive barrier layer 24 may comprise a respective topsurface having an inner periphery and an outer periphery within thehorizontal plane including the top surface of the second bonding-leveldielectric layer.

In one embodiment, the entirety or a major portion of each second coppermaterial portion 26 may be located at or below the horizontal planeincluding the top surface of the second bonding-level dielectric layer.In one embodiment, the middle of each second copper material portion 26is recessed farther than its edges. Thus, for each second bonding pad 28located within a respective second pad cavity, a vertical distancebetween a concave top surface of the second copper material portion 26and the horizontal plane increases with a lateral distance from arespective most proximal point within a periphery of the pad cavity thatis located within the horizontal plane, i.e., with a lateral distancefrom a top periphery of the second pad cavity. In other words, thefarther a point within a concave top surface of a second copper materialportion 26 is laterally from the periphery of the second pad cavity, thefarther the point is vertically from the horizontal plane.

The maximum dishing depth, i.e., the maximum distance between theconcave top surface of each second copper material portion 26 from thehorizontal plane including the top surface of the second bonding-leveldielectric layer, may be in a range from 1 nm to 30 nm, such as from 2nm to 10 nm, although lesser and greater maximum dishing depths may alsobe employed. In one embodiment, at least 50%, such as from 80% to 100%,of the area of the top surface of each second copper material portion 26may be recessed below the horizontal plane including the top surface ofthe second bonding-level dielectric layer (which comprises thelogic-level dielectric material layer 770).

Generally, the second semiconductor die 200 comprises secondsemiconductor devices, second metal interconnect structures embedded insecond dielectric material layers and electrically connected to thesecond semiconductor devices, and at least one second bonding pad 28embedded in a second bonding-level dielectric layer and electricallyconnected to one of the second metal interconnect structures.

The second bonding pad 28 comprises a second conductive barrier layer 24comprising a second conductive barrier material having a lowerelectrochemical potential than copper and a second copper materialportion 26 laterally surrounded by the second conductive barrier layer24. Optionally, a suitable pre-anneal bonding process may be performed,for example, at a temperature of about 150 degrees Celsius.

Referring to FIG. 3A, the first substrate including the plurality offirst semiconductor dies 100 and the second substrate including theplurality of second semiconductor dies 200 can be aligned to each otherfor bonding. In this case, the first bonding pads 18 and the secondbonding pads 28 can face each other. In the illustrated example, thefirst semiconductor dies 100 can be memory dies 900, the secondsemiconductor dies 200 can be logic dies 700, the first bonding pads 18can be memory-side bonding pads 988, and the second bonding pads 28 canbe logic-side bonding pads 788.

The first bonding-level dielectric layer is brought into contact withthe second bonding-level dielectric layer while each mating pair of afirst bonding pad 18 and a second bonding pad 28 remains aligned to eachother. Thus, the convex first bonding pads 18 having respective convexfirst copper material portions 16 are aligned to respective concavesecond bonding pads having respective concave second copper materialportions 26. A cavity, which is herein referred to as a bonding cavity,may be formed between each mating pair of a first bonding pad 18 and asecond bonding pad 28.

In one embodiment, the volume of each bonding cavity may be in a rangefrom 0.01% to 0.5%, such as from 0.03% 0.3% of the combined volume ofthe mating pair of a first copper material portion 16 and a secondcopper material portion 26. Generally, each cavity may include a volumeof a moat-shaped groove 14G and a volume between a convex surface of afirst copper material portion 16 and a concave surface of a secondcopper material portion 26.

Referring to FIG. 3B, an anneal process can be performed at an elevatedtemperature to induce copper-to-copper bonding between each mating pairof a first bonding pad 18 and a second bonding pad 28. The elevatedtemperature of the anneal process may be in a range from 300 degreesCelsius to 450 degrees Celsius, such as from 350 degrees Celsius to 425degrees Celsius.

The first copper material portions 16 and the second copper materialportions 26 expand in volume during the anneal process, and are bondedto a respective mating copper material portion. In one embodiment, awafer-to-wafer bonding process may be performed to bond an array offirst semiconductor dies 100 on the first substrate 108 to an array ofsecond semiconductor dies 200 on the second substrate 208.

Generally, copper-to-copper bonding can be induced between the secondcopper material portions 26 and the first copper material portions 16such that each second bonding pad 28 can be bonded to a respective oneof the first bonding pad 18, and each first bonding pad 18 can be bondedto a respective one of the second bonding pads 28. In one embodiment, atleast 80%, such from 85% to 100%, and/or from 90% to 99%, of a bondinginterface between the first bonding pad 18 and the second bonding pad 28within each bonded pair of a first bonding pad 18 and a second bondingpad 28 may be formed on a side of the second semiconductor die 200relative to a horizontal plane including an interface between the firstbonding dielectric layer and the second bonding dielectric layer afterbonding the second bonding pads 28 to the first bonding pad 18.

In one embodiment, a bonding interface between the first bonding pads 18and the second bonding pads 28 between each bonded pair of a firstbonding pad 18 and a second bonding pad 28 comprises a non-planar (i.e.,curved) interface at which a convex surface of the first copper materialportion 16 contacts a concave surface of the second copper materialportion 26. In one embodiment, the entirety of a periphery of the convexsurface of the first copper material portion 16 in a bonded pair of afirst bonding pad 18 and a second bonding pad 28 may be adjoined to asurface of the first bonding-level dielectric layer (970 or 770).

In one embodiment, the first conductive barrier layer 14 in a bondedpair of a first bonding pad 18 and a second bonding pad 28 may bevertically spaced from the second bonding pad 28 by a peripheral portionof the first copper material portion 16 that contacts a sidewall of thefirst bonding-level dielectric layer (which comprises the memory-sidebonding-level dielectric layer 970 in the illustrated example). Theperipheral portion of the first copper material portion 16 may fill thevolume of the moat-shaped groove 14G in the first conductive barrierlayer 14. Thus, the bonding pads 18 and 28 of the first embodiment forma good bond, even in the case of partial lateral misalignment.

In contrast, in prior art bonded assemblies containing opposing convexbonding pads surrounded by respective moat-shaped grooves, there may beinsufficient contact between the bonding pads in case of the partiallateral misalignment of the opposing bonding pads. In other words, ifonly the moat-shaped grooves overlap each other, then there may not besufficient copper filling of both grooves to form a sufficient bond.Likewise, in other prior art bonded assemblies containing opposingconcave bonding pads, there may be insufficient copper filling in themiddle of the bonding pads which forms a void in the middle of thebonding interface between opposing convex bonding pads. The voiddegrades the quality of the bond.

In one embodiment, the first conductive barrier layer 14 comprises avertically-extending portion contacting a sidewall of the firstbonding-level dielectric layer (such as the memory-side bonding-leveldielectric layer 970) and having a contoured top surface thatcontinuously extends around the first copper material portion 16 andhaving a concave vertical cross-sectional profile (i.e., the verticalcross-sectional profile of a mot-shaped groove 14G). In one embodiment,a point of the concave top surface laterally midway between an innersidewall and an outer sidewall of the concave top surface is more distalfrom a horizontal plane at which the first bonding-level dielectriclayer contacts the second bonding-level dielectric layer than a point ofthe inner sidewall that is mot proximal to the horizontal plane, andthan a point of the outer sidewall that is most proximal to thehorizontal plane. This is due to the “U-shaped” vertical cross-sectionalprofile of the moat-shaped groove 14G overlying the annular top surfaceof the first conductive barrier layer 14.

In one embodiment, a vertically extending portion of the firstconductive barrier layer 14 in a bonded pair of a first bonding pad 18and a second bonding pad 28 comprises a moat-shaped groove 14G thatlaterally surrounds the first copper material portion 16 and having aconcave profile. A peripheral portion of the first copper materialportion 16 fills the moat-shaped groove 14G, and is disposed between thefirst conductive barrier layer 14 and the second bonding pad 28.

In one embodiment, at least 80%, such as from 85% to 100%, and/or from90% to 99%, of the bonding interface between the first bonding pads 18and the second bonding pads 28 may be located on a side of the secondsemiconductor die 200 with respect to a horizontal plane including aninterface between the first bonding-level dielectric layer and thesecond bonding-level dielectric layer.

In one embodiment, the first conductive barrier layer 14 in a bondedpair of a first bonding pad 18 and a second bonding pad 28 is verticallyspaced from the second bonding pad 28 by the first copper materialportion 16, and the second conductive barrier layer 24 is in directcontact with the first copper material portion 16.

In one embodiment, the first conductive barrier layer 14 consistsessentially of a material selected from cobalt, tantalum, or tantalumnitride. In one embodiment, the second conductive barrier layer 24consists essentially of a material selected from ruthenium, titanium, ortitanium nitride.

In one embodiment, the second bonding-level dielectric layer is indirect contact with the first bonding-level dielectric layer at ahorizontal plane, and a horizontal surface of a vertically-extendingportion of the second conductive barrier layer 24 is located within thehorizontal plane. In one embodiment, an annular surface of avertically-extending portion of the first conductive barrier layer 14that faces the second semiconductor die 200 and is most proximal to thesecond semiconductor die 200 is vertically spaced from the horizontalplane by a peripheral portion of the first copper material portion 16,i.e., by a sub-portion of the first copper material portion 16 thatfills a moat-shaped groove 14G. In one embodiment, the annular surfacecomprises a non-planar grooved surface having a concave verticalcross-sectional profile, and the non-planar grooved surface is contactedentirely by the first copper material portion 16.

Referring to FIG. 3C, the memory-side substrate 908 may optionally bethinned from the backside by grinding, polishing, an anisotropic etch,or an isotropic etch. The thinning process can continue until horizontalportions of the through-substrate liners 386 are removed, and horizontalsurfaces of the through-substrate via structures (if present) 388 arephysically exposed. Generally, end surfaces of the through-substrate viastructures 388 can be physically exposed by thinning the backside of thememory-side substrate 908, which may be the substrate of a memory die.The thickness of the memory-side substrate 908 after thinning may be ina range from 1 micron to 30 microns, such as from 2 microns to 15microns, although lesser and greater thicknesses can also be employed.

An optional backside insulating layer 930 may be formed on the backsideof the memory-side substrate 908. The backside insulating layer 930includes an insulating material such as silicon oxide. The thickness ofthe backside insulating layer 930 can be in a range from 50 nm to 500nm, although lesser and greater thicknesses can also be employed. Aphotoresist layer (not shown) may be applied over the backsideinsulating layer 930, and may be lithographically patterned to formopening over areas of the through-substrate via structures 388. An etchprocess can be performed to form via cavities through the backsideinsulating layer 930 underneath each opening in the photoresist layer. Atop surface of a through-substrate via structure 388 can be physicallyexposed at the bottom of each via cavity through the backside insulatinglayer 930.

At least optional one metallic material can be deposited into theopenings through the backside insulating layer 930 and over the planarsurface of the backside insulating layer 930 to form a metallic materiallayer. The at least one metallic material can include copper, aluminum,ruthenium, cobalt, molybdenum, and/or any other metallic material thatmay be deposited by physical vapor deposition, chemical vapordeposition, electroplating, vacuum evaporation, or other depositionmethods. For example, a metallic nitride liner material (such as TiN,TaN, or WN) may be deposited directly on the physically exposed surfacesof the through-substrate via structures 388, on sidewalls of theopenings through the backside insulating layer 930, and over thephysically exposed planar surface of the backside insulating layer 930.The thickness of the metallic nitride liner material can be in a rangefrom 10 nm to 100 nm, although lesser and greater thicknesses can alsobe employed. At least one metallic fill material such as copper oraluminum can be deposited over the metallic nitride liner material. Inone embodiment, the at least one metallic fill material can include astack of a high-electrical-conductivity metal layer (such as a copperlayer or an aluminum layer) and an underbump metallization (UBM) layerstack for bonding a solder ball thereupon. Exemplary UBM layer stacksinclude, but are not limited to, an Al/Ni/Au stack, an Al/Ni/Cu stack, aCu/Ni/Au stack, a Cu/Ni/Pd stack, a Ti/Ni/Au stack, a Ti/Cu/Ni/Au stack,a Ti—W/Cu stack, a Cr/Cu stack, and a Cr/Cu/Ni stack. The thickness ofthe metallic material layer over the planar horizontal surface of thebackside insulating layer 930 can be in a range from 0.5 microns to 10microns, such as from 1 micron to 5 microns, although lesser and greaterthicknesses can also be employed.

The at least one metallic fill material and the metallic material layercan be subsequently patterned to form discrete backside bonding pads 936contacting a respective one of the through-substrate via structures 388.The backside bonding pads 936 can function as external bonding pads thatcan be employed to electrically connect various nodes of within thememory die 900 and the logic die 700 to external nodes, such as bondingpads on a packaging substrate or C4 bonding pads of anothersemiconductor die. For example, solder material portions 938 can beformed on the backside bonding pads 936, and a C4 bonding process or awire bonding process can be performed to electrically connect thebackside bonding pads 936 to external electrically active nodes.

Generally, backside bonding pads 936 can be formed on a backside surfaceof the memory die 900 (which may be a memory die) that is located on anopposite side of the bonding interfaces with the logic die 700.Through-substrate via structures 388 can vertically extend through thememory die 900, and can provide electrical connection between thebackside bonding pads 936 and a subset of the bonding pads (18, 28).

In an alternative aspect of the first embodiment shown in FIG. 3D, thehorizontal semiconductor channel layer 10, the through-substrate liners386, the through-substrate via structures 388, the through-memory-leveldielectric liner 486 and/or the through-memory-level via structure 488may be omitted. In this alternative configuration, the entire firstsubstrate 108 is removed rather than thinned to expose the tips of thememory opening fill structures 58. After removing the first substrate108, the memory films at the exposed tips of the memory opening fillstructures 58 are removed by selective etching to expose the tips of thesemiconductor channels in the memory opening fill structures 58. A dopedsemiconductor source layer 110 is formed in contact with the exposedtips of the semiconductor channels. A conductive source line (e.g.,source contact) 112 is then formed on the doped semiconductor sourcelayer 110.

Referring to FIG. 4A, a second configuration of the first exemplarystructure is illustrated. The second configuration of the firstexemplary structure can be derived from the first configuration of thefirst exemplary structure illustrated in FIG. 3A by forming thememory-side bonding pads 988 as second bonding pads 28, and by formingthe logic-side bonding pads 788 as first bonding pads 18. In otherwords, the memory-side bonding pads 988 are formed as combinations of arespective second conductive barrier layer 24 and a respective secondcopper material portion 28 employing the second chemical mechanicalplanarization process described above, and the logic-side bonding pads788 are formed as combinations of a respective first conductive barrierlayer 14 and a respective first copper material portion 18 employing thefirst chemical mechanical planarization process described above.

Each of the first conductive barrier layers 14 in the secondconfiguration of the first exemplary structure may be formed with thesame material composition and with the same geometrical features as thefirst conductive barrier layers 14 in the first configuration of thefirst exemplary structure as described above. Each of the first coppermaterial portions 16 in the second configuration of the first exemplarystructure may be formed with the same material composition and with thesame geometrical features as the first copper material portion 16 in thefirst configuration of the first exemplary structure as described above.Each of the second conductive barrier layers 24 in the secondconfiguration of the first exemplary structure may be formed with thesame material composition and with the same geometrical features as thesecond conductive barrier layers 24 in the first configuration of thefirst exemplary structure as described above. Each of the second coppermaterial portions 26 in the second configuration of the first exemplarystructure may be formed with the same material composition and with thesame geometrical features as the second copper material portions 26 inthe first configuration of the first exemplary structure as describedabove.

Referring to FIG. 4B, the processing steps described with reference toFIG. 3B may be performed to induce copper-to-copper bonding between eachmating pair of a respective first copper material portion 16 and arespective second copper material portion 26. Dielectric-to-dielectricbonding (such as silicon oxide-to-silicon oxide bonding) may beperformed simultaneously with the copper-to-copper bonding between thefirst bonding-level dielectric layer and the second bonding-leveldielectric layer. The bonded pairs of a respective first copper materialportion 16 and a respective second copper material portion 26 may havethe same geometry as in the first configuration of the first exemplarystructure described with reference to FIG. 3B.

Referring to FIGS. 4C and 4D, the processing steps described withreference to respective FIGS. 3C and 3D may be performed as describedabove.

Referring to FIG. 5 , a third configuration of a logic die 700 isillustrated in which the size of opposing bonding pads differs from eachother. Generally, the third configuration of the logic die 700 can bederived from the first configuration of the logic die 700 that isillustrated with reference to FIGS. 2C and 2D by increasing the size ofeach second bonding pad 28. Specifically, the lateral dimensions of thesecond bonding pads 28 can be selected such that the area of the topsurface of each second copper material portion 26 is designed to includethe entirety of the area of the top surface a respective first bondingpad 18 to be subsequently bonded thereto. Thus, the periphery of theconcave top surface of each second bonding pad 28 may have a shape in aplan view that is laterally offset outward from a mirror image of theperiphery of the outer sidewall of the first conductive barrier layer 14of the first bonding pad 18 to which the second bonding pad 28 is to besubsequently bonded.

Referring to FIG. 6A, the processing steps of FIG. 3A can be performedwith any needed changes in view of the increase in the size of thesecond bonding pads 28, such that the second bonding pads 28 face thefirst bonding pads 18. In one embodiment, the annular top surfaces ofthe second conductive barrier layers 24 of the second bonding pads 28may directly contact the top surface of the first bonding-leveldielectric layer (such as the memory-side bonding-level dielectric layer970). In one embodiment, an entirety of a top surface of the secondconductive barrier layer 26 of a second bonding pad 28 may contact ahorizontal surface of the first bonding-level dielectric layer.

Referring to FIG. 6B, the processing steps of FIG. 3B can be performedto induce metal-to-metal bonding between each mating pair of a firstcopper material portion 16 and a second coper material portion 26.Dielectric-to-dielectric bonding (such as silicon oxide-to-silicon oxidebonding) may be performed simultaneously with the copper-to-copperbonding between the first bonding-level dielectric layer and the secondbonding-level dielectric layer. Generally, the bonded pairs of arespective first copper material portion 16 and a respective secondcopper material portion 26 may have the same geometry, or similargeometry, as in the first configuration of the first exemplary structuredescribed with reference to FIG. 3B. In the third configuration of thefirst exemplary structure, the entirety of a bonding surface of thefirst copper material portion 16 in a bonded pair of a first bonding pad18 and a second bonding pad 28 may be in contact with a bonding surfaceof the second copper material portion 26. In one embodiment, an annularperipheral surface of the second copper material portion 26 of a secondbonding pad 28 may be in contact with the first bonding-level dielectriclayer (which may comprise a memory-side bonding-level dielectric layer970). In one embodiment, an entirety of a top surface of the secondconductive barrier layer 24 in a second bonding pad 28 may be in contactwith the first bonding-level dielectric layer.

In this configuration, the convex first bonding pads 18 have a smallerwidth than the concave second bonding pads 28, such that the edges ofthe second copper material portions 26 fill the grooves 14G. Thisimproves the bonding quality between the opposing bonding pads.Subsequently, the processing steps of FIG. 3C or 3D may be performed tothin the backside of the memory-side substrate 908 (or to remove itcompletely) and to form various backside bonding structures or acombination of the doped semiconductor source layer 110 and source line112.

Referring to FIG. 7A, a fourth configuration of the first exemplarystructure is illustrated. The fourth configuration of the firstexemplary structure can be derived from the third configuration of thefirst exemplary structure illustrated in FIG. 6A by forming thememory-side bonding pads 988 as second bonding pads 28, and by formingthe logic-side bonding pads 788 as first bonding pads 18. In otherwords, the memory-side bonding pads 988 are formed as combinations of arespective second conductive barrier layer 24 and a respective secondcopper material portion 28 employing the second chemical mechanicalplanarization process described above, and the logic-side bonding pads788 are formed as combinations of a respective first conductive barrierlayer 14 and a respective first copper material portion 18 employing thefirst chemical mechanical planarization process described above.

Referring to FIG. 7B, the processing steps described with reference toFIG. 6B may be performed to induce copper-to-copper bonding between eachmating pair of a respective first copper material portion 16 and arespective second copper material portion 26. Dielectric-to-dielectricbonding (such as silicon oxide-to-silicon oxide bonding) may beperformed simultaneously with the copper-to-copper bonding between thefirst bonding-level dielectric layer and the second bonding-leveldielectric layer. The bonded pairs of a respective first copper materialportion 16 and a respective second copper material portion 26 may havethe same geometry as in the third configuration of the first exemplarystructure described with reference to FIG. 6B. Subsequently, theprocessing steps described with reference to FIGS. 3C and 3D may beperformed to thin the backside of the memory-side substrate 908 (or toremove it completely) and to form various backside bonding structures ora combination of the doped semiconductor source layer 110 and sourceline 112.

Referring to the first embodiment, and all drawings associated with thefirst exemplary structure, a bonded assembly comprises a firstsemiconductor die 100 comprising first semiconductor devices (920 or720) and a first bonding pad 18. The first bonding pad comprises a firstcopper material portion 16 and a first conductive barrier layer 14comprising a first conductive barrier material having a higherelectrochemical potential than copper located between the firstsemiconductor devices (920 or 720) and the first copper material portion16. The bonded assembly also includes a second semiconductor die 200comprising second semiconductor devices (720 or 920) and a secondbonding pad 28. The second bonding pad comprises a second coppermaterial portion 26 and a second conductive barrier layer 24 comprisinga second conductive barrier material having a lower electrochemicalpotential than copper located between the second semiconductor devices(720 or 920) and the second copper material portion 26. The secondbonding pad is bonded to the first bonding pad.

In one embodiment, a bonding interface between the first bonding pads 18and the second bonding pads 28 comprises a non-planar interface at whicha convex surface of the first copper material portion 16 contacts aconcave surface of the second copper material portion 26.

In one embodiment, the first semiconductor die 100 further comprises atleast one first dielectric material layer, first metal interconnectstructures embedded in the at least one first dielectric material layerand electrically connected to the first semiconductor devices, and afirst bonding-level dielectric layer, wherein the first bonding pad isembedded in the first bonding-level dielectric layer and electricallyconnected to at least one of the first metal interconnect structures.The second semiconductor die further comprises at least one seconddielectric material layer, second metal interconnect structures embeddedin the at least one second dielectric material layer and electricallyconnected to the second semiconductor devices, and a secondbonding-level dielectric layer, wherein the second bonding pad isembedded in the second bonding-level dielectric layer and electricallyconnected to at least one of the second metal interconnect structures.

In one embodiment, an entirety of a periphery of the convex surface ofthe first copper material portion 16 is adjoined to a surface of thefirst bonding-level dielectric layer (970 or 770). In one embodiment,the first conductive barrier layer 14 is vertically spaced from thesecond bonding pad 28 by a peripheral portion of the first coppermaterial portion 16 that contacts a sidewall of the first bonding-leveldielectric layer (970 or 770).

In one embodiment, the first conductive barrier layer 14 comprises avertically-extending portion contacting a sidewall of the firstbonding-level dielectric layer (970 or 770) and having a contoured topsurface that continuously extends around the first copper materialportion 16 and having a concave vertical cross-sectional profile; and apoint of the concave top surface laterally midway between an innersidewall and an outer sidewall of the concave top surface is more distalfrom a horizontal plane at which the first bonding-level dielectriclayer (970 or 770) contacts the second bonding-level dielectric layer(770 or 970) than a point of the inner sidewall that is mot proximal tothe horizontal plane, and than a point of the outer sidewall that ismost proximal to the horizontal plane.

In one embodiment, a vertically extending portion of the firstconductive barrier layer 14 comprises a moat-shaped groove 14G thatlaterally surrounds the first copper material portion 16 and having aconcave profile; and a peripheral portion of the first copper materialportion 16 fills the moat-shaped groove 14G and is disposed between thefirst conductive barrier layer 14 and the second bonding pad 28. In oneembodiment, at least 80% of the bonding interface between the firstbonding pads 18 and the second bonding pads 28 is located on a side ofthe second semiconductor die 200 with respect to a horizontal planeincluding an interface between the first bonding-level dielectric layer(970 or 770) and the second bonding-level dielectric layer (770 or 970).

In one embodiment, the first conductive barrier layer 14 is verticallyspaced from the second bonding pad 28 by the first copper materialportion 16, and the second conductive barrier layer 24 is in directcontact with the first copper material portion 16. In one embodiment, anentirety of a bonding surface of the first copper material portion 16 isin contact with a bonding surface of the second copper material portion26. In one embodiment, an annular peripheral surface of the secondcopper material portion 26 is in contact with the first bonding-leveldielectric layer (970 or 770), and an entirety of a top surface of thesecond conductive barrier layer 24 is in contact with the firstbonding-level dielectric layer (970 or 770).

In one embodiment, the first conductive barrier layer 14 consistsessentially of a material selected from cobalt, tantalum, or tantalumnitride. In one embodiment, the second conductive barrier layer 24consists essentially of a material selected from ruthenium, titanium, ortitanium nitride.

In one embodiment, the second bonding-level dielectric layer (770 or970) is in direct contact with the first bonding-level dielectric layer(970 or 770) at a horizontal plane; a horizontal surface of avertically-extending portion of the second conductive barrier layer 24is located within the horizontal plane; and an annular surface of avertically-extending portion of the first conductive barrier layer 14that faces the second semiconductor die 200 and is most proximal to thesecond semiconductor die 200 is vertically spaced from the horizontalplane by a peripheral portion of the first copper material portion 16.In one embodiment, the annular surface comprises a non-planar groovedsurface having a concave vertical cross-sectional profile, and thenon-planar grooved surface is contacted entirely by the first coppermaterial portion 16.

The combination of a convex bonding surface of a first copper materialportion 16 and a concave bonding surface of a second copper materialportion 26 reduces the volume of a cavity that needs to be filledthrough volume expansion of the copper material portions (16, 26) duringa bonding anneal process. By reducing the volume of cavities to befilled during the bonding anneal process, the copper-to-copper bondingbetween mating pairs of copper material portions (16, 26) can be formedwith greater adhesion strength and with less defects, thereby increasingthe bonding yield.

Referring to FIG. 8A, a first configuration of a memory die 900according to a second embodiment of the present disclosure isillustrated. The memory die 900 can be employed to form first-typebonding pads, or first bonding pads thereupon. In one embodiment, thememory-side substrate 908 may be a portion of a commercially availablesilicon wafer having a thickness in a range from 500 microns to 1 mm. Inone embodiment, a plurality of first semiconductor dies 100 can beprovided on a first wafer.

The first configuration of the memory die 900 in the second embodimentof the present disclosure may be derived from the first configuration ofthe memory die 900 in the first embodiment of the present disclosureillustrated in FIG. 1A by forming a first conductive barrier layer 13Land a first copper layer 15L. The first conductive barrier layer 13L andthe first copper layer 15L are employed to form first bonding pads insubsequent processing steps. The first conductive barrier layer 13L maycomprise a memory-side conductive barrier layer 984L. The first copperlayer 15L may comprise a memory-side copper layer 986L.

According to an aspect of the present disclosure, the materialcomposition and the thickness of the first conductive barrier layer 13Lare selected such that at least 10% of the volume fraction of a coppermaterial portion in each first bonding pad may include (200) coppergrains, where (200) is the Miller Index of the plane of the coppergrains. The at least 10% of the volume fraction may be formed inpolycrystalline copper after an anneal at an elevated temperature, suchas an anneal at 150 degrees Celsius, for example. As used herein,crystallographic orientations of copper grains in a copper layer referto the crystallographic plane within the copper layer that generates aBragg peak in an x-ray scan in which the incidence angle and thereflection angle are the same, which is typically referred to as a θ:2θscan. The incidence angle is measured between the direction of theincident X-ray beam and the horizontal plane that is perpendicular tothe growth direction of the copper layer. The reflection angle ismeasured between the direction of the reflected X-ray beam and thehorizontal plane that is perpendicular to the growth direction of thecopper layer. In a θ:2θ scan, the detector angle 2θ (as measured betweenthe direction of the incident beam and the reflected beam) is double theincidence angle θ that is measured between the incident beam and thesample surface, such as a horizontally-extending portion of the topsurface of the first copper layer 15L that is parallel to the topsurface of the first bonding-level dielectric layer. Thus, (200) coppergrains are copper grains that generate a (200) peak in a θ:2θ X-rayscan. Similarly, (110) copper grains are copper grains that generate a(110) peak in a θ:2θ X-ray scan. (111) copper grains are copper grainsthat generate (111) peak in a θ:2θ X-ray scan. Generally, the (200)copper grains grow along a direction that is perpendicular to the [100]crystallographic orientation direction of copper, and therefore, include(100) crystallographic planes as horizontal planes. The (110) coppergrains grow along a direction that is perpendicular to the [110]crystallographic orientation direction of copper, and therefore, include(110) crystallographic planes as horizontal planes. The (111) coppergrains grow along a direction that is perpendicular to the [111]crystallographic orientation direction of copper, and therefore, include(111) crystallographic planes as horizontal planes.

Generally, slow recrystallization of electroplated copper results information of a predominant fraction of copper grains as (111) coppergrains. In contrast, formation of (200) copper grains by annealingelectroplated copper at any significant volume fraction is moredifficult to achieve. According to an aspect of the present disclosure,the material composition and the thickness of the first conductivebarrier layer 13L can be selected such that each first copper pad mayinclude (200) copper grains at a volume fraction not less than 10% afteran anneal process at 150 degrees Celsius prior to a bonding process. Thepresent inventors found material compositions and/or thickness rangesthat result formation of (200) copper grains at a volume fraction of atleast 10% within first bonding pads that are formed after a firstchemical mechanical planarization process, and preferably by performinga subsequent anneal at an elevated temperature, such as 100 to 200degrees Celsius, such as 150 degrees Celsius.

Specifically, in one embodiment, the first conductive barrier layer 13Lcomprises a titanium layer 13A that is formed directly on, and thus isin direct contact with the first bonding-level dielectric layer (whichmay comprise the memory-side bonding-level dielectric layer 970). Thefirst conductive barrier layer 13L has a thickness of at least 10 nm.For example, the titanium layer 13A is in direct contact with the firstcopper material portion 15 and has a thickness greater than 15 nm. Thethickness of the titanium layer 13A may be in a range from 16 nm to 30nm.

In a first example, which is herein referred to as Option 1, the firstconductive barrier layer 13L may consist of the titanium layer 13Ahaving a thickness greater than 15 nm, such as a thickness in a rangefrom 16 nm to 30 nm. In this case, the first copper layer 15L can beformed directly on the titanium layer 13A, which is the entirety of thefirst conductive barrier layer 13L.

In a second example, which is herein referred to as Option 2, the firstconductive barrier layer 13L comprises a tantalum layer 13B that isformed between the titanium layer 13A and the first copper layer 15L. Inthis case, the first copper layer 15L can be formed directly on thetantalum layer 13B. The thickness of the first conductive barrier layer13L may be in a range from 10 nm to 60 nm, the thickness of the titaniumlayer 13A may be in a range from 5 nm to 30 nm, and the thickness of thetantalum layer 13B may be in a range from 5 nm to 30 nm, such as from 5nm to 20 nm.

The thickness of the first copper layer 15L, as measured over ahorizontal top surface of the first bonding-level dielectric layer, maybe in a range from 300 nm to 6 microns, such as from 600 nm to 3microns, although lesser and greater thicknesses may also be employed.The first copper layer 15L as deposited may be polycrystalline,amorphous or substantially amorphous, i.e., may include crystallographicgrains at a volume fraction less than 10%, such as less than 5%, and/orless than 2%. The first copper layer 15L may be deposited using a twostep deposition process which includes first depositing a copper seedlayer by physical vapor deposition (e.g., sputtering) followed bydepositing a copper fill layer on the copper seed layer by plating(e.g., electroplating).

Referring to FIG. 8B, a first chemical mechanical polishing (CMP)process can be performed to remove portions of the first copper layer15L (which may comprise the memory-side copper layer 986L) and the firstconductive barrier layer 13L (which may comprise the memory-sideconductive barrier layer 984L) from above the top surface of the firstbonding-level dielectric layer (which may comprise the memory-sidebonding-level dielectric layer 970). Each remaining portion of the firstcopper layer 15L comprises the first copper material portion 15. Eachremaining portion of the first conductive barrier layer 13L comprises afirst conductive barrier layer 13. Each first copper material portion 15is a memory-side copper material portion 986. Each first conductivebarrier layer 13L is a memory-side conductive barrier layer 984 embeddedwithin the memory-side bonding dielectric layer 970. Each contiguouscombination of a first conductive barrier layer 13 and a first coppermaterial portion 15 constitutes a first bonding pad 17, which is amemory-side bonding pad 988.

An anneal at an elevated temperature may be performed to induceformation of crystalline grains within the first copper materialportions 15. Generally, the crystallization characteristics of thincopper films, such as copper films having a thickness less than 3,000 nmand/or less than 1,000 nm, is different from crystallizationcharacteristics of thick copper films, and generates more (111) grainsthan thick copper films. According to an aspect of the presentdisclosure, the material composition and the thickness of the firstconductive barrier layers 13 are selected such that more than 10% of thevolume fraction of all copper material within each first copper materialportion 15 includes (200) copper grains after a low temperature annealat a relatively low temperature, such as an anneal at a temperature of150 degrees Celsius. The duration of the anneal at the elevatedtemperature may be in a range from 10 minutes to 600 minutes, such asfrom 30 minutes to 300 minutes, although lesser and greater durationsmay also be employed. As discussed above, formation of more than 10% ofthe volume fraction of all copper material within each first coppermaterial portion 15 as (200) copper grains may be achieved under severalconditions. For example, the first conductive barrier layer 13 in eachfirst bonding pad 17 may comprises a titanium layer 13A in directcontact with the first bonding-level dielectric layer. In one example,the titanium layer 13A in each first bonding pad 17 may be in directcontact with the first copper material portion 15 and may have athickness greater than 15 nm. In this example, the first copper materialportion 15 in contact with the titanium layer 13A may have a concave top(i.e., bonding) surface, as discussed above with respect to the firstembodiment. In another example, the first conductive barrier layer 13 ineach first bonding pad 17 further comprises a tantalum layer 13Bdisposed between the titanium layer 13A and the first copper materialportion 15. In this example, the first copper material portion 15 incontact with the tantalum layer 13B may have a convex top (i.e.,bonding) surface, as discussed above with respect to the firstembodiment.

First bonding pads 17 are embedded in a first bonding-level dielectriclayer (such as the memory-side bonding-level dielectric layer 970) andelectrically connected to a respective one of the first metalinterconnect structures (such as the memory-side metal interconnectstructures 960). Each of the first bonding pads 17 comprises a firstconductive barrier layer 13 including a material composition or amaterial stack that induces subsequent formation of more than 10% involume fraction of (200) copper grains in the first copper materialportions 15 after a subsequent anneal process. Each of the first bondingpads 17 comprises a first copper material portion 15 at least partiallylaterally surrounded by the first conductive barrier layer 13. A topsurface of the first copper portion 15 in each first bonding pad 17 maybe vertically recessed relative to the horizontal plane including thetop surface of the first bonding-level dielectric layer.

Generally, a first semiconductor die 100 comprises first semiconductordevices, first metal interconnect structures embedded in firstdielectric material layers and electrically connected to the firstsemiconductor devices, and a first bonding pad 17 embedded in a firstbonding-level dielectric layer and electrically connected to one of thefirst metal interconnect structures. The first bonding pad 17 comprisesa first conductive barrier layer 13 and a first copper material portion15 laterally surrounded by the first conductive barrier layer 13 andincluding (200) copper grains at a volume fraction not less than 10%.

Referring to FIG. 9A, a first configuration of a logic die 700 forformation of a second exemplary structure is illustrated. Second-typebonding pads, which are also referred to as second bonding pads, can besubsequently formed on the logic die 700. In this case, the logic die700 can be referred to as a second-type semiconductor die, or as asecond semiconductor die 200. The logic die 700 includes a logic-sidesubstrate 708, logic-side semiconductor devices 720 overlying thelogic-side substrate 708, logic-side dielectric material layers 750located on the logic-side semiconductor devices, and logic-side metalinterconnect structures 760 embedded in the logic-side dielectricmaterial layers 750. In one embodiment, the logic-side substrate 708 maybe a commercially available silicon wafer having a thickness in a rangefrom 500 microns to 2 mm. In one embodiment, a plurality of secondsemiconductor dies 200 may be provided on a second wafer.

The first configuration of the logic die 700 in the second embodiment ofthe present disclosure may be derived from the first configuration ofthe logic die 700 in the first embodiment of the present disclosureillustrated in FIG. 2A by forming a second conductive barrier layer 23Land a second copper layer 25L. The second conductive barrier layer 23Land the second copper layer 25L are employed to form second bonding padsin subsequent processing steps. The second conductive barrier layer 23Lmay be embodied as a logic-side conductive barrier layer 784L. Thesecond copper layer 25L may be embodied as a logic-side copper layer786L.

According to an aspect of the present disclosure, the materialcomposition and/or the thickness of the second conductive barrier layer23L are selected such that at least 10% of the volume fraction of acopper material portion in each second bonding pad may include (200)copper grains upon an anneal at an elevated temperature. Specifically,the second conductive barrier layer 23L comprises a titanium layer 23Athat is formed directly on, and thus is in direct contact with thesecond bonding-level dielectric layer (which may comprise the logic-sidebonding-level dielectric layer 770). The thickness of the secondconductive barrier layer 23L is at least 10 nm. The titanium layer 23Ais in direct contact with the second copper material portion 25 and hasa thickness greater than 15 nm. The thickness of the titanium layer 23Amay be in a range from 16 nm to 30 nm.

In a first example, which is herein referred to as Option I, the secondconductive barrier layer 23L may consist of the titanium layer 23Ahaving a thickness greater than 15 nm, such as a thickness in a rangefrom 16 nm to 30 nm. In this case, the second copper layer 25L can beformed directly on the titanium layer 23A, which constitutes theentirety of the second conductive barrier layer 23L.

In a second example, which is herein referred to as Option II, thesecond conductive barrier layer 23L comprises a tantalum layer 23B thatis formed between the titanium layer 23A and the second copper layer25L. The thickness of the second conductive barrier layer 23 may be in arange from 10 nm to 60 nm, the thickness of the titanium layer 23A maybe in a range from 5 nm to 30 nm, and the thickness of the tantalumlayer 23B may be in a range from 5 nm to 30 nm, such as from 5 nm to 20nm.

The thickness of the second copper layer 25L, as measured over ahorizontal top surface of the second bonding-level dielectric layer, maybe in a range from 300 nm to 6 microns, such as from 600 nm to 3microns, although lesser and greater thicknesses may also be employed.The second copper layer 25L as deposited may be polycrystalline,amorphous, or substantially amorphous.

Referring to FIG. 9B, a second chemical mechanical polishing (CMP)process can be performed to remove portions of the second copper layer25L (comprising the logic-side copper layer 786L) and the secondconductive barrier layer 23L (comprising the logic-side conductivebarrier layer 784L) from above the top surface of the secondbonding-level dielectric layer (comprising the logic-side bonding-leveldielectric layer 770). Each remaining portion of the second copper layer25L comprises the second copper material portion 25. Each remainingportion of the second conductive barrier layer 23L comprises a secondconductive barrier layer 23. Each second copper material portion 25 is alogic-side copper material portion 786. Each second conductive barrierlayer 23 is a logic-side conductive barrier layer 784 embedded withinthe logic-side bonding dielectric layer 770. Each contiguous combinationof a second conductive barrier layer 23 and a second copper materialportion 25 constitutes a second bonding pad 27, which is a logic-sidebonding pad 788.

An anneal at an elevated temperature may be performed to induceformation of crystal grains within the second copper material portions25. As described above, the material composition and/or the thickness ofthe second conductive barrier layers 23 are selected such that at least10% of the volume fraction of all copper material within each secondcopper material portion 25 includes (200) copper grains after a lowtemperature anneal described above. In one example, the secondconductive barrier layer 23 in each second bonding pad 27 may comprisesa titanium layer 23A in direct contact with the second bonding-leveldielectric layer. The titanium layer 23A in each second bonding pad 27may be in direct contact with the second copper material portion 25 andmay have a thickness greater than 15 nm. In another example, the secondconductive barrier layer 23 in each second bonding pad 27 comprises atantalum layer 23B disposed between the titanium layer 23A and thesecond copper material portion 25.

Second bonding pads 27 are embedded in a second bonding-level dielectriclayer (such as the logic-side bonding-level dielectric layer 770) andelectrically connected to a respective one of the second metalinterconnect structures (such as the logic-side metal interconnectstructures 760). Each of the second bonding pads 27 comprises a secondconductive barrier layer 23 including a material composition or amaterial stack that induces subsequent formation of at least 10% involume fraction of (200) copper grains in the second copper materialportions 25 upon a subsequent anneal process. Each of the second bondingpads 27 comprises a second copper material portion 25 at least partiallylaterally surrounded by the second conductive barrier layer 23. A topsurface of the second copper portion 25 in each second bonding pad 27may be vertically recessed relative to the horizontal plane includingthe top surface of the second bonding-level dielectric layer.

Generally, a second semiconductor die 200 comprises second semiconductordevices, second metal interconnect structures embedded in seconddielectric material layers and electrically connected to the secondsemiconductor devices, and a second bonding pad 27 embedded in a secondbonding-level dielectric layer and electrically connected to one of thesecond metal interconnect structures. The second bonding pad 27comprises a second conductive barrier layer 23 and a second coppermaterial portion 25 laterally surrounded by the second conductivebarrier layer 23 and including (200) copper grains at a volume fractionof at least 10%.

Referring to FIG. 10A, the first wafer including the plurality of firstsemiconductor dies 100 and the second wafer including the plurality ofsecond semiconductor dies 200 can be aligned to each other for bonding.In this case, the front side of each wafer including the first bondingpads 17 or the second bonding pads 27 can face each other. The secondbonding pads 27 can be arranged in a mirror image pattern of the firstbonding pads 17, and the first wafer and the second wafer can be alignedsuch that each second bonding pad faces a respective first bonding padand vice versa. In the illustrated example, the first semiconductor dies100 can be memory dies 900, the second semiconductor dies 200 can belogic dies 700, the first bonding pads 17 can be memory-side bondingpads 988, and the second bonding pads 27 can be logic-side bonding pads788.

In one configuration in which the first and the second embodiments arecombined one of the first bonding pad 17 or the second bonding pad 27has a concave vertical cross-sectional profile, and the other one of thefirst bonding pad 17 or the second bonding pad 27 has a convex verticalcross-sectional profile. Specifically, one of the first bonding pad 17or the second bonding pad 27 may have the Option I configuration wherethe copper material portion directly contacts the titanium layer to formthe concave vertical cross-sectional profile. The other one of the firstbonding pad 17 or the second bonding pad 27 may have the Option IIconfiguration where the copper material portion directly contacts thetantalum layer of the titanium-tantalum layer stack to form the convexvertical cross-sectional profile. The bonding of concave bonding pad tothe opposing convex bonding pad may form the non-planar bondinginterface and improve the bonding quality, as described above.

The first and second dies are brought into contact with each other suchthat each mating pair of a first bonding pad 17 and a second bonding pad27 are aligned to each other. A cavity, which is herein referred to as abonding cavity, may be formed between each mating pair of a firstbonding pad 17 and a second bonding pad 27. In one embodiment, thevolume of each bonding cavity may be in a range from 0.01% to 0.5%, suchas from 0.03% 0.3% of the combined volume of the mating pair of a firstcopper material portion 15 and a second copper material portion 25.

Referring to FIG. 10B, a thermal anneal process can be performed at anelevated temperature to induce copper-to-copper bonding between eachmating pair of a first bonding pad 17 and a second bonding pad 27. Theelevated temperature of the thermal anneal process may be in a rangefrom 300 degrees Celsius to 450 degrees Celsius, such as from 350degrees Celsius to 425 degrees Celsius. The first copper materialportions 15 and the second copper material portions 25 expand in volumeduring the thermal anneal process, and contact and are bonded to arespective mating copper material portion. In one embodiment, a bondingprocess may be performed to bond an array of first semiconductor dies100 on a first substrate to an array of second semiconductor dies 200 ona second substrate.

Generally, copper-to-copper bonding can be induced between the secondcopper material portions 25 and the first copper material portions 15such that each second bonding pad 27 can be bonded to a respective oneof the first bonding pad 17, and each first bonding pad 17 can be bondedto a respective one of the second bonding pads 27. According to anaspect of the present disclosure, the first copper material portions 15and the second copper material portions 25 include (200) copper grainsat a volume fraction of at least 10%, such as from 10% to 80% and/orfrom 15% to 70%, and/or from 20% to 60%. The (200) copper grains providea greater linear volume expansion along the grain growth direction(i.e., along the vertical direction perpendicular to the bondinginterface) than directions that are perpendicular to the grain growthdirection. In other words, the volume expansion of copper grains is notisotropic, but is the greatest along the growth directions of the (200)copper grains. For example, the ratio of the volume expansion rate (perunit temperature change) along the grain growth direction (i.e., avertical direction) for (200) copper grains is believed to be greaterthan the volume expansion rate (per unit temperature change) along thegrain growth direction for (110) and (111) copper grains.

Referring back to FIG. 10B, the higher the volume fraction of (200)copper grains in the first copper material portion 15 and in the secondcopper material portion 25, the greater the volume expansion of thefirst copper material portions 15 and the second copper materialportions 25, and the lower the probability of insufficient contactbetween mating pairs of a respective first copper material portions 15and the second copper material portions 25. By increasing the volumefraction of (200) copper grains above 10%, embodiments of the presentdisclosure increase copper volume expansion for the purpose ofcopper-to-copper bonding along the direction that is substantiallyperpendicular to the bonding interfaces, and improves the quality ofcopper-to-copper bonding.

Generally, the second bonding pads 27 can be bonded to the first bondingpads 17 by inducing copper-to-copper bonding between the second coppermaterial portions 25 and the first copper material portions 15. In oneembodiment, the second copper material portion includes (200) coppergrains at a volume fraction of at least 10% (such as a volume fractionin a range from 10% to 80% and/or from 15% to 70%, and/or from 20% to60%) prior to and after bonding the second bonding pads 27 to the firstbonding pads 17. In one embodiment, the first conductive barrier layer13 in each bonded pair of a first bonding pad 17 and a second bondingpad 27 includes a layer stack including a titanium layer 13A and atantalum layer 13B that contacts the first copper material portion 15,or a titanium layer 13A having a thickness not less than 15 nm. In oneembodiment, the second conductive barrier layer 23 includes a layerstack including a titanium layer 23A and a tantalum layer 23B thatcontacts the second copper material portion 25, or a titanium layer 23Ahaving a thickness not less than 15 nm.

Referring to FIG. 10C, the processing steps of FIG. 3C can be performedto thin the backside of the memory-side substrate 908, and to formvarious backside bonding structures.

Alternatively, referring to FIG. 10D, a doped semiconductor source layer110 is formed in contact with the exposed tips of the semiconductorchannels, and a conductive source line (e.g., source contact) 112 isthen formed on the doped semiconductor source layer 110, as describedwith regard to FIG. 3D.

Referring to FIG. 11A, a second configuration of a logic die 700according to a second embodiment of the present disclosure isillustrated. The second configuration of the logic die 700 can bederived from the first configuration of the logic die 700 illustrated inFIG. 10A by employing a second conductive barrier layer 33L having adifferent material composition than the second conductive barrier layer23L in the first configuration of the logic die 700 in the secondembodiment of the present disclosure as illustrated in FIG. 9A. Thesecond conductive barrier layer 33L is formed as a logic-side conductivebarrier layer 784L. A second copper layer 35L can be formed on thesecond conductive barrier layer 33L. The second copper layer 35L isformed as a logic-side copper layer 786L.

According to an aspect of the present disclosure, the materialcomposition and the thickness of the second conductive barrier layer 33Lare selected such that at least 95% of the volume fraction of a coppermaterial portion in each second bonding pad may include (111) coppergrains, such as after an anneal at an elevated temperature, such as atemperature of 100 to 200 degrees Celsius, for example 150 degreesCelsius. In some embodiments, the second conductive barrier layer 33Lcomprises a tantalum layer 33A in direct contact with the secondbonding-level dielectric layer (such as the logic-side bonding-leveldielectric layer 770) without contacting an underlying titanium layer.In some embodiments, the second conductive barrier layer 33L comprises atitanium layer 33B having a thickness of 10 nm or less in direct contactwith the second copper material portion 35. In some embodiments, thesecond conductive barrier layer 33L is a stack of an underlying tantalumlayer 33A and an overlying titanium layer 33B having a thickness of 10nm or less in direct contact with the second copper material portion 35.

In a first example, which is herein referred to as Option A, the secondconductive barrier layer 33L consists of a tantalum layer 33A having athickness greater than 10 nm, such as a thickness in a range from 15 nmto 30 nm. In this case, the second copper layer 35L can be formeddirectly on the tantalum layer 33A, which comprises the entirety of thesecond conductive barrier layer 23L.

In a second example, which is herein referred to as Option B, the secondconductive barrier layer 23L comprises a stack of a tantalum layer 33Aand a titanium layer 33B. The tantalum layer 33A is in direct contactwith the second bonding-level dielectric layer (such as the logic-sidebonding-level dielectric layer 770). The titanium layer 33B is in directcontact with the second copper material portion 35. The thickness of thetitanium layer 33B is less than the thickness of the tantalum layer 33A.The thickness of the second conductive barrier layer 33L may be in arange from 15 nm to 30 nm, the thickness of the tantalum layer 33A maybe in a range from 15 nm to 30 nm, and the thickness of the titaniumlayer 33B may be in a range from 0 nm to 10 nm, such as from 1 nm to 6nm and/or from 2 nm to 4 nm.

In a third example, which is herein referred to as Option C, the secondconductive barrier layer 33L consists of a titanium layer having athickness of 10 nm or less, such as from 1 nm to 6 nm and/or from 2 nmto 4 nm. In this case, the second copper layer 35L can be formeddirectly on the titanium layer 33B, which comprises the entirety of thesecond conductive barrier layer 23L.

The thickness of the second copper layer 35L, as measured over ahorizontal top surface of the second bonding-level dielectric layer, maybe in a range from 300 nm to 6 microns, such as from 600 nm to 3microns, although lesser and greater thicknesses may also be employed.The second copper layer 35L as deposited may be polycrystalline,amorphous, or substantially amorphous.

Referring to FIG. 11B, a second chemical mechanical polishing (CMP)process can be performed to remove portions of the second copper layer35L (comprising the logic-side copper layer 786L) and the secondconductive barrier layer 33L (comprising the logic-side conductivebarrier layer 784L) from above the top surface of the secondbonding-level dielectric layer (comprising the logic-side bonding-leveldielectric layer 770). Each remaining portion of the second copper layer35L comprises the second copper material portion 35. Each remainingportion of the second conductive barrier layer 33L comprises a secondconductive barrier layer 33. Each second copper material portion 35 is alogic-side copper material portion 786. Each second conductive barrierlayer 33 is a logic-side conductive barrier layer 784 embedded withinthe logic-side bonding dielectric layer 770. Each contiguous combinationof a second conductive barrier layer 33 and a second copper materialportion 35 constitutes a second bonding pad 37, which is a logic-sidebonding pad 788.

An anneal at an elevated temperature may be performed to induceformation of crystal grains within the second copper material portions35. According to an aspect of the present disclosure, the materialcomposition and/or the thickness of the second conductive barrier layers33 are selected such that at least 95% of the volume fraction of allcopper material within each second copper material portion 35 includes(111) copper grains. The duration of the anneal at the elevatedtemperature of 100 to 200 degrees Celsius may be in a range from 30minutes to 600 minutes, such as from 30 minutes to 300 minutes, althoughlesser and greater durations may also be employed. Without wishing to bebound by a particular theory, the present inventors believe that copperformed directly on thin titanium barrier layers (e.g., having athickness or 10 or less) or directly on tantalum barrier layers withoutan underlying titanium barrier layer have a predominant (111)orientation in which at least 95 volume percent of all grains have a(111) orientation.

Second bonding pads 37 are embedded in a second bonding-level dielectriclayer (such as the logic-side bonding-level dielectric layer 770) andelectrically connected to a respective one of the second metalinterconnect structures (such as the logic-side metal interconnectstructures 760). Each of the second bonding pads 37 comprises a secondconductive barrier layer 33 including a material composition or amaterial stack that induces subsequent formation of at least 95% involume fraction of (111) copper grains in the second copper materialportions 35 upon a subsequent anneal process. Thus, at least 95%, suchas from 95% to 100%, and/or from 96% to 99%, of the volume fraction of acopper material portion in each second bonding pad 35 may include (111)copper grains upon an anneal at an elevated temperature (which may beabout 150 degrees Celsius). Each of the second bonding pads 37 comprisesa second copper material portion 35 at least partially laterallysurrounded by the second conductive barrier layer 33. A top surface ofthe second copper portion 35 in each second bonding pad 37 may bevertically recessed relative to the horizontal plane including the topsurface of the second bonding-level dielectric layer.

Generally, a second semiconductor die 200 comprises second semiconductordevices, second metal interconnect structures embedded in seconddielectric material layers and electrically connected to the secondsemiconductor devices, and a second bonding pad 37 embedded in a secondbonding-level dielectric layer and electrically connected to one of thesecond metal interconnect structures. The second bonding pad 37comprises a second conductive barrier layer 33 and a second coppermaterial portion 35 laterally surrounded by the second conductivebarrier layer 33 and including (111) copper grains at a volume fractionof at least 95%.

Referring to FIG. 12A, a second configuration of the second exemplarystructure according to the second embodiment of the present disclosureis illustrated. A first wafer can be provided, which includes aplurality of first semiconductor dies 100 that includes multipleinstances of the first semiconductor die 100 as illustrated in FIG. 8C.A second wafer can be provided, which includes a plurality of secondsemiconductor dies 200 that includes multiple instances of the secondsemiconductor die as illustrated in FIG. 11B. The first wafer and thesecond wafer can be aligned to each other for bonding. In this case, thefront side of each wafer including the first bonding pads 17 or thesecond bonding pads 37 can face each other. The second bonding pads 37can be arranged in a mirror image pattern of the first bonding pads 17,and the first wafer and the second wafer can be aligned such that eachsecond bonding pad faces a respective first bonding pad and vice versa.In the illustrated example, the first semiconductor dies 100 can bememory dies 900, the second semiconductor dies 200 can be logic dies700, the first bonding pads 17 can be memory-side bonding pads 988, andthe second bonding pads 37 can be logic-side bonding pads 788.

The first bonding-level dielectric layer can be brought into contactwith the second bonding-level dielectric layer while each mating pair ofa first bonding pad 17 and a second bonding pad 37 remains aligned toeach other. A cavity, which is herein referred to as a bonding cavity,may be formed between each mating pair of a first bonding pad 17 and asecond bonding pad 37. In one embodiment, the volume of each bondingcavity may be in a range from 0.01% to 0.5%, such as from 0.03% 0.3% ofthe combined volume of the mating pair of a first copper materialportion 15 and a second copper material portion 35.

Referring to FIG. 12B, a thermal anneal process can be performed at anelevated temperature to induce copper-to-copper bonding between eachmating pair of a first bonding pad 17 and a second bonding pad 37. Theelevated temperature of the thermal anneal process may be in a rangefrom 300 degrees Celsius to 450 degrees Celsius, such as from 350degrees Celsius to 425 degrees Celsius. The first copper materialportions 15 and the second copper material portions 35 expand in volumeduring the thermal anneal process, and contact and are bonded to arespective mating copper material portion.

Generally, copper-to-copper bonding can be induced between the secondcopper material portions 35 and the first copper material portions 15such that each second bonding pad 37 can be bonded to a respective oneof the first bonding pad 17, and each first bonding pad 17 can be bondedto a respective one of the second bonding pads 37. According to anaspect of the present disclosure, the first copper material portions 15include (200) copper grains at a volume fraction of at least 10%, suchas from 10% to 80% and/or from 15% to 70%, and/or from 20% to 60%.According to another aspect of the present disclosure, the second coppermaterial portions 35 include (111) copper grains at a volume fraction ofat least 95%, such as from 95% to 100%, and/or from 96% to 99%.

The (200) copper grains provide a greater liner volume expansion alongthe grain growth direction (i.e., along the vertical direction) thandirections that are perpendicular to the grain growth direction asdiscussed above. The (111) copper grain provide greater surfacediffusivity than the (200) copper grains. The higher surface diffusivityof the (111) copper grains promote copper diffusion along the bondinginterfaces between the first copper material portions 15 and the secondcopper material portions 35 to enhance the adhesion at the bondinginterface during the bonding process.

Generally, the second bonding pads 37 can be bonded to the first bondingpads 17 by inducing copper-to-copper bonding between the second coppermaterial portions 35 and the first copper material portions 15. In oneembodiment, the first conductive barrier layer 13 in each bonded pair ofa first bonding pad 17 and a second bonding pad 37 includes a layerstack including a titanium layer 13A and a tantalum layer 13B thatcontacts the first copper material portion 15; or a titanium layer 13Ahaving a thickness not less than 15 nm. In one embodiment, the secondcopper material portion 35 in each bonded pair of a first bonding pad 17and a second bonding pad 37 includes (111) copper grains at a volumefraction not less than 95% prior to and after bonding the second bondingpad 37 to the first bonding pad 17. In one embodiment, the secondconductive barrier layer 33 in each bonded pair of a first bonding pad17 and a second bonding pad 37 consists of: a layer stack including atantalum layer 33A and a titanium layer 33B that contacts the secondcopper material portion 35; a titanium layer 33B having a thickness lessthan 10 nm; or a tantalum layer 33A without an underlying titaniumlayer.

Referring to FIG. 12C, the processing steps of FIG. 3C can be performedto thin the backside of the memory-side substrate 908, and to formvarious backside bonding structures. Alternatively, a dopedsemiconductor source layer 110 is formed in contact with the exposedtips of the semiconductor channels, and a conductive source line (e.g.,source contact) 112 is then formed on the doped semiconductor sourcelayer 110, as described with regard to FIGS. 3D and 10D.

Referring to FIG. 13A, a third configuration of a memory die 900according to a second embodiment of the present disclosure isillustrated. The third configuration of the memory 900 may be derivedfrom the first configuration of the memory die 900 illustrated in FIG.8A by employing the second conductive barrier layer 33L in lieu of thefirst conductive barrier layer 13L. The second conductive barrier layer33L is formed as a memory-side conductive barrier layer 984L. A secondcopper layer 35L can be formed on the second conductive barrier layer33L. The second copper layer 35L is formed as a memory-side copper layer986L.

According to an aspect of the present disclosure, the materialcomposition and the thickness of the second conductive barrier layer 33Lare selected such that at least 95% of the volume fraction of a coppermaterial portion in each second bonding pad may include (111) coppergrains, such as after an anneal at an elevated temperature, for exampleat 150 degrees Celsius. The second conductive barrier layer 33L may havethe same material composition and the same thickness range as discussedabove.

Referring to FIG. 13B, a second chemical mechanical polishing (CMP)process can be performed to remove portions of the second copper layer35L (comprising the memory-side copper layer 986L) and the secondconductive barrier layer 33L (comprising the memory-side conductivebarrier layer 984L) from above the top surface of the secondbonding-level dielectric layer (comprising the memory-side bonding-leveldielectric layer 970). Each remaining portion of the second copper layer35L comprises the second copper material portion 35. Each remainingportion of the second conductive barrier layer 33L comprises a secondconductive barrier layer 33. Each second copper material portion 35 is amemory-side copper material portion 986. Each second conductive barrierlayer 33 is a memory-side conductive barrier layer 984 embedded withinthe memory-side bonding dielectric layer 970. Each contiguouscombination of a second conductive barrier layer 33 and a second coppermaterial portion 35 constitutes a second bonding pad 37, which is amemory-side bonding pad 988.

An anneal at an elevated temperature may be performed to induceformation of crystal grains within the second copper material portions35. According to an aspect of the present disclosure, the materialcomposition and/or the thickness of the second conductive barrier layers33 are selected such at least 95% of the volume fraction of all coppermaterial within each second copper material portion 35 includes (111)copper grains, such as after a low temperature anneal at a relativelylow temperature, such as an anneal at a temperature of 150 degreesCelsius, as described above.

Second bonding pads 37 are embedded in a second bonding-level dielectriclayer (such as the memory-side bonding-level dielectric layer 970) andelectrically connected to a respective one of the second metalinterconnect structures (such as the memory-side metal interconnectstructures 960). Each of the second bonding pads 37 comprises a secondconductive barrier layer 33 including a material composition or amaterial stack that induces subsequent formation of at least 95% involume fraction of (111) copper grains in the second copper materialportions 35. Thus, at least 95%, such as from 95% to 100%, and/or from96% to 99% of the volume fraction of a copper material portion in eachsecond bonding pad 35 may include (111) copper grains. Each of thesecond bonding pads 37 comprises a second copper material portion 35laterally surrounded by the second conductive barrier layer 33. A topsurface of the second copper portion 35 in each second bonding pad 37may be vertically recessed relative to the horizontal plane includingthe top surface of the second bonding-level dielectric layer.

Generally, the second semiconductor die 200 comprises secondsemiconductor devices, second metal interconnect structures embedded insecond dielectric material layers and electrically connected to thesecond semiconductor devices, and a second bonding pad 37 embedded in asecond bonding-level dielectric layer and electrically connected to oneof the second metal interconnect structures. The second bonding pad 37comprises a second conductive barrier layer 33 and a second coppermaterial portion 35 at least partially laterally surrounded by thesecond conductive barrier layer 33 and including (111) copper grains ata volume fraction of at least 95%.

Referring to FIG. 14A, a third configuration of the second exemplarystructure according to the second embodiment of the present disclosureis illustrated. A first wafer can be provided, which includes aplurality of first semiconductor dies 100. The first semiconductor die100 may be the same as the logic 700 illustrated in FIG. 9B. A secondwafer can be provided, which includes a plurality of secondsemiconductor dies 200 that includes multiple instances of the memorydie 900 illustrated in FIG. 13B. The first wafer and the second wafercan be aligned to each other for bonding. In this case, the bonding pads27 (which may be the same as bonding pad 17) and 37 can face each other.The first bonding-level dielectric layer can be brought into contactwith the second bonding-level dielectric layer while each mating pair ofbonding pads 27 and 37 remains aligned to each other.

Referring to FIG. 14B, the processing steps of FIG. 12B can be performedto induce bonding between the bonding pads 27 and 37, as describedabove.

Referring to FIG. 14C, the processing steps of FIG. 3C can be performedto thin the backside of the memory-side substrate 908, and to formvarious backside bonding structures. Alternatively, a dopedsemiconductor source layer 110 is formed in contact with the exposedtips of the semiconductor channels, and a conductive source line (e.g.,source contact) 112 is then formed on the doped semiconductor sourcelayer 110, as described with regard to FIGS. 3D and 10D.

Referring to the first, second and third configurations of the secondexemplary structure and FIGS. 8A to 14C related thereto, a bondedassembly comprises a first semiconductor die 100 comprising firstsemiconductor devices (920 or 720) and a first bonding pad 17. The firstbonding pad comprises a first copper material portion 15 containing(200) copper grains at a volume fraction of at least 10% and a firstconductive barrier layer 13 located between the first semiconductordevices and the first copper material portion. The bonded assembly alsoincludes a second semiconductor die 200 comprising second semiconductordevices (720 or 920) and a second bonding pad (27 or 37). The secondbonding pad comprises a second copper material portion (25 or 35) and asecond conductive barrier layer (23 or 33) located between the secondsemiconductor devices and the second copper material portion. The secondbonding pad is bonded to the first bonding pad.

In one embodiment, the first conductive barrier layer 13 comprises atitanium layer 13A having a thickness greater than 15 nm. In anotherembodiment, the first conductive barrier layer 13 comprises a stack of atantalum layer 13B and a titanium layer 13A, wherein the tantalum layeris disposed between the titanium layer and the first copper materialportion 15.

In the first configuration of the second embodiment illustrated in FIGS.8A to 10D, the second copper material portion 25 contains (200) coppergrains at a volume fraction of at least 10%. In one embodiment, thesecond conductive barrier layer 23 comprises a titanium layer 23A havinga thickness greater than 15 nm. In another embodiment, the secondconductive barrier layer 23 comprises a stack of a tantalum layer 23Band a titanium layer 23A, wherein the tantalum layer is disposed betweenthe titanium layer and the first copper material portion 25.

In the second and third configurations of the second embodimentillustrated in FIGS. 9A to 14C, the second copper material portion 35contains (111) copper grains at a volume fraction of at least 95%. Inone embodiment, the second conductive barrier layer 33 comprises atantalum layer 33A in direct contact with the second copper materialportion 35. In another embodiment, the second conductive barrier layer33 comprises a titanium layer 33A having a thickness not greater than 10nm in direct contact with the second copper material portion 35. Inanother embodiment, the second conductive barrier layer 33 comprises astack of a tantalum layer 33B and a titanium layer 33A, wherein thetitanium layer is disposed between the tantalum layer and the firstcopper material portion 35.

It is believed that the (200) copper grains provide higher meanexpansion distance per unit temperature change (e.g., per degreeCelsius) than the (110) copper grains and the (111) copper grains. Incontrast, it is also believed that the (111) copper grains providehigher surface diffusivity than (110) copper grains and (200) coppergrains. Embodiments utilizing at least 10% in volume fraction of (200)copper grains in a first copper material portion 15 and a second coppermaterial portion 25 utilize increased volume expansion of the (200)copper grains along the vertical direction (along the directionperpendicular to the bonding interfaces) to provide enhancedcopper-to-copper bonding between copper material portions (15, 25).Embodiments utilizing at least 10% in volume fraction of (200) coppergrains in a first copper material portion 15 and at least 95% in volumefraction of (111) copper grains in a second copper material portion 35utilize the combination of increased volume expansion from the firstcopper material portion 15 and enhanced surface diffusivity provided bythe second copper material portion 35 to provide enhancedcopper-to-copper bonding between copper material portions (15, 35).

Although the foregoing refers to particular embodiments, it will beunderstood that the disclosure is not so limited. It will occur to thoseof ordinary skill in the art that various modifications may be made tothe disclosed embodiments and that such modifications are intended to bewithin the scope of the disclosure. Compatibility is presumed among allembodiments that are not alternatives of one another. The word“comprise” or “include” contemplates all embodiments in which the word“consist essentially of” or the word “consists of” replaces the word“comprise” or “include,” unless explicitly stated otherwise. Where anembodiment using a particular structure and/or configuration isillustrated in the present disclosure, it is understood that the presentdisclosure may be practiced with any other compatible structures and/orconfigurations that are functionally equivalent provided that suchsubstitutions are not explicitly forbidden or otherwise known to beimpossible to one of ordinary skill in the art. All of the publications,patent applications and patents cited herein are incorporated herein byreference in their entirety.

1. A bonded assembly, comprising: a first semiconductor die comprisingfirst semiconductor devices and a first bonding pad, wherein the firstbonding pad comprises a first copper material portion and a firstconductive barrier layer comprising a first conductive barrier materialhaving a higher electrochemical potential than copper located betweenthe first semiconductor devices and the first copper material portion;and a second semiconductor die comprising second semiconductor devicesand a second bonding pad, wherein the second bonding pad comprises asecond copper material portion and a second conductive barrier layercomprising a second conductive barrier material having a lowerelectrochemical potential than copper located between the secondsemiconductor devices and the second copper material portion; whereinthe second bonding pad is bonded to the first bonding pad.
 2. The bondedassembly of claim 1, wherein a bonding interface between the firstbonding pads and the second bonding pads comprises a non-planarinterface at which a convex surface of the first copper material portioncontacts a concave surface of the second copper material portion.
 3. Thebonded assembly of claim 2, wherein: the first semiconductor die furthercomprises: at least one first dielectric material layer; first metalinterconnect structures embedded in the at least one first dielectricmaterial layer and electrically connected to the first semiconductordevices; and a first bonding-level dielectric layer, wherein the firstbonding pad is embedded in the first bonding-level dielectric layer andelectrically connected to at least one of the first metal interconnectstructures; and the second semiconductor die further comprises: at leastone second dielectric material layer; second metal interconnectstructures embedded in the at least one second dielectric material layerand electrically connected to the second semiconductor devices; and asecond bonding-level dielectric layer, wherein the second bonding pad isembedded in the second bonding-level dielectric layer and electricallyconnected to at least one of the second metal interconnect structures.4. The bonded assembly of claim 3, wherein: an entirety of a peripheryof the convex surface of the first copper material portion is adjoinedto a surface of the first bonding-level dielectric layer; and the firstconductive barrier layer is vertically spaced from the second bondingpad by a peripheral portion of the first copper material portion thatcontacts a sidewall of the first bonding-level dielectric layer.
 5. Thebonded assembly of claim 3, wherein: the first conductive barrier layercomprises a vertically-extending portion contacting a sidewall of thefirst bonding-level dielectric layer and having a contoured top surfacethat continuously extends around the first copper material portion andhaving a concave vertical cross-sectional profile; and a point of theconcave top surface laterally midway between an inner sidewall and anouter sidewall of the concave top surface is more distal from ahorizontal plane at which the first bonding-level dielectric layercontacts the second bonding-level dielectric layer than a point of theinner sidewall that is mot proximal to the horizontal plane, and than apoint of the outer sidewall that is most proximal to the horizontalplane.
 6. The bonded assembly of claim 3, wherein: a verticallyextending portion of the first conductive barrier layer comprises amoat-shaped groove that laterally surrounds the first copper materialportion and having a concave profile; and a peripheral portion of thefirst copper material portion fills the moat-shaped groove and isdisposed between the first conductive barrier layer and the secondbonding pad.
 7. The bonded assembly of claim 3, wherein at least 80% ofthe bonding interface between the first bonding pad and the secondbonding pad is located on a side of the second semiconductor die withrespect to a horizontal plane including an interface between the firstbonding-level dielectric layer and the second bonding-level dielectriclayer.
 8. The bonded assembly of claim 3, wherein: the second bondingpad is wider than the first bonding pad; an entirety of a bondingsurface of the first copper material portion is in contact with abonding surface of the second copper material portion; an annularperipheral surface of the second copper material portion is in contactwith the first bonding-level dielectric layer; and an entirety of a topsurface of the second conductive barrier layer is in contact with thefirst bonding-level dielectric layer.
 9. The bonded assembly of claim 3,wherein: the second bonding-level dielectric layer is in direct contactwith the first bonding-level dielectric layer at a horizontal plane; ahorizontal surface of a vertically-extending portion of the secondconductive barrier layer is located within the horizontal plane; and anannular surface of a vertically-extending portion of the firstconductive barrier layer that faces the second semiconductor die and ismost proximal to the second semiconductor die is vertically spaced fromthe horizontal plane by a peripheral portion of the first coppermaterial portion.
 10. The bonded assembly of claim 9, wherein theannular surface comprises a non-planar grooved surface having a concavevertical cross-sectional profile, and the non-planar grooved surface iscontacted entirely by the first copper material portion.
 11. The bondedassembly of claim 1, wherein: the first conductive barrier layer isvertically spaced from the second bonding pad by the first coppermaterial portion; and the second conductive barrier layer is in directcontact with the first copper material portion.
 12. The bonded assemblyof claim 1, wherein: the first conductive barrier layer consistsessentially of a material selected from cobalt, tantalum, or tantalumnitride; and the second conductive barrier layer consists essentially ofa material selected from ruthenium, titanium, or titanium nitride. 13.The bonded assembly of claim 1, wherein: the first copper materialportion is at least partially laterally surrounded by the firstconductive barrier layer; and the second copper material portion is atleast partially laterally surrounded by the second conductive barrierlayer.
 14. A method of forming a bonded assembly, comprising: providinga first semiconductor die comprising first semiconductor devices, firstmetal interconnect structures embedded in first dielectric materiallayers and electrically connected to the first semiconductor devices,and a first bonding pad embedded in a first bonding-level dielectriclayer and electrically connected to one of the first metal interconnectstructures, wherein the first bonding pad comprises a first conductivebarrier layer comprising a first conductive barrier material having ahigher electrochemical potential than copper and a first copper materialportion at least partially laterally surrounded by the first conductivebarrier layer; providing a second semiconductor die comprising secondsemiconductor devices, second metal interconnect structures embedded insecond dielectric material layers and electrically connected to thesecond semiconductor devices, and a second bonding pad embedded in asecond bonding-level dielectric layer and electrically connected to oneof the second metal interconnect structures, wherein the second bondingpad comprises a second conductive barrier layer comprising a secondconductive barrier material having a lower electrochemical potentialthan copper and a second copper material portion at least partiallylaterally surrounded by the second conductive barrier layer; and bondingthe second bonding pad to the first bonding pad by inducingcopper-to-copper bonding between the second copper material portion andthe first copper material portion.
 15. The method of claim 14, wherein:a top surface of the first copper material portion is formed with aconvex vertical cross-sectional profile; and a top surface of the secondcopper material portion is formed with a concave verticalcross-sectional profile.
 16. The method of claim 15, wherein the firstbonding pad is formed by: forming a first pad cavity in the firstbonding-level dielectric layer; forming a layer of the first conductivebarrier material and a first copper layer in the first pad cavity; andperforming a first chemical mechanical polishing process, wherein aremaining portion of the first copper layer comprises the first coppermaterial portion and a remaining portion of the layer of the firstconductive barrier material comprises the first conductive barrierlayer, and wherein a moat-shaped groove in which a concave top surfaceof the first conductive barrier layer is vertically recessed relative toa top surface of the first copper material portion is formed around thefirst copper material portion.
 17. The method of claim 15, wherein: atleast 50% of a top surface of the first copper material portionprotrudes outward from a horizontal plane including a top surface of thefirst bonding-level dielectric layer prior to bonding the second bondingpad to the first bonding pad; and at least 80% of a bonding interfacebetween the first bonding pad and the second bonding pad is formed on aside of the second semiconductor die relative to a horizontal planeincluding an interface between the first bonding dielectric layer andthe second bonding dielectric layer after bonding the second bonding padto the first bonding pad.
 18. The method of claim 15, wherein the secondbonding pad is formed by: forming a pad cavity in the secondbonding-level dielectric layer; forming a layer of the second conductivebarrier material and a second copper layer in the pad cavity; andperforming a chemical mechanical polishing process.
 19. The method ofclaim 18, wherein: a remaining portion of the second copper layercomprises the second copper material portion and a remaining portion ofthe layer of the second conductive barrier material comprises the secondconductive barrier layer; a top surface of the second conductive barrierlayer is formed within a horizontal plane including a top surface of thesecond bonding-level dielectric layer; and an entirety of the secondcopper material portion is located at or below the horizontal plane suchthat a vertical distance between a concave top surface of the secondcopper material portion and the horizontal plane increases with alateral distance from a respective most proximal point within aperiphery of the pad cavity that is located within the horizontal plane.20. The method of claim 14, wherein: the first conductive barrier layerconsists essentially of a material selected from cobalt, tantalum, ortantalum nitride; and the second conductive barrier layer consistsessentially of a material selected from ruthenium, titanium, or titaniumnitride.